diff --git a/docs/diff/es2015.core.d.ts.md b/docs/diff/es2015.core.d.ts.md
index f4bec93..88ea98e 100644
--- a/docs/diff/es2015.core.d.ts.md
+++ b/docs/diff/es2015.core.d.ts.md
@@ -126,14 +126,13 @@ Index: es2015.core.d.ts
    /**
     * The value of the largest integer n such that n and n + 1 are both exactly representable as
     * a Number value.
-@@ -273,45 +282,26 @@
+@@ -273,49 +282,20 @@
    /**
     * Copy the values of all of the enumerable own properties from one or more source objects to a
     * target object. Returns the target object.
     * @param target The target object to copy to.
 -   * @param source The source object from which to copy properties.
-+   * @param sources One or more source objects from which to copy properties
-    */
+-   */
 -  assign<T, U>(target: T, source: U): T & U;
 -
 -  /**
@@ -154,39 +153,35 @@ Index: es2015.core.d.ts
 -   * @param source3 The third source object from which to copy properties.
 -   */
 -  assign<T, U, V, W>(
-+  assign<T, Ts extends readonly any[]>(
-     target: T,
+-    target: T,
 -    source1: U,
 -    source2: V,
 -    source3: W
 -  ): T & U & V & W;
-+    ...sources: Ts
-+  ): CheckNonNullable<
-+    T,
-+    First<
-+      UnionToIntersection<
-+        | [T]
-+        | {
-+            [K in keyof Ts]: [Ts[K]];
-+          }[number]
-+      >
-+    >
-+  >;
- 
-   /**
+-
+-  /**
 -   * Copy the values of all of the enumerable own properties from one or more source objects to a
 -   * target object. Returns the target object.
 -   * @param target The target object to copy to.
--   * @param sources One or more source objects from which to copy properties
--   */
+    * @param sources One or more source objects from which to copy properties
+    */
 -  assign(target: object, ...sources: any[]): any;
--
--  /**
++  assign<T, Ts extends readonly any[]>(
++    target: CheckNonNullable<T>,
++    ...sources: Ts
++  ): Intersect<[T, ...Ts]>;
+ 
+   /**
     * Returns an array of all symbol properties found directly on object o.
     * @param o Object to retrieve the symbols from.
     */
-   getOwnPropertySymbols(o: any): symbol[];
-@@ -326,16 +316,23 @@
+-  getOwnPropertySymbols(o: any): symbol[];
++  getOwnPropertySymbols<T>(o: CheckNonNullable<T>): symbol[];
+ 
+   /**
+    * Returns the names of the enumerable string properties and methods of an object.
+    * @param o Object that contains the properties and methods. This can be an object that you created or an existing Document Object Model (DOM) object.
+@@ -326,16 +306,23 @@
     * Returns true if the values are the same value, false otherwise.
     * @param value1 The first value.
     * @param value2 The second value.
@@ -212,7 +207,7 @@ Index: es2015.core.d.ts
  
  interface ReadonlyArray<T> {
    /**
-@@ -346,20 +343,25 @@
+@@ -346,20 +333,25 @@
     * immediately returns that element value. Otherwise, find returns undefined.
     * @param thisArg If provided, it will be used as the this value for each invocation of
     * predicate. If it is not provided, undefined is used instead.
@@ -249,7 +244,7 @@ Index: es2015.core.d.ts
  
    /**
     * Returns the index of the first element in the array where predicate is true, and -1
-@@ -369,11 +371,11 @@
+@@ -369,11 +361,11 @@
     * findIndex immediately returns that element index. Otherwise, findIndex returns -1.
     * @param thisArg If provided, it will be used as the this value for each invocation of
     * predicate. If it is not provided, undefined is used instead.
@@ -264,7 +259,7 @@ Index: es2015.core.d.ts
  }
  
  interface RegExp {
-@@ -433,26 +435,17 @@
+@@ -433,26 +425,17 @@
     * same as the corresponding elements of this object (converted to a String) starting at
     * endPosition – length(this). Otherwise returns false.
     */
diff --git a/docs/diff/es2017.object.d.ts.md b/docs/diff/es2017.object.d.ts.md
index 2101f1f..9ce6196 100644
--- a/docs/diff/es2017.object.d.ts.md
+++ b/docs/diff/es2017.object.d.ts.md
@@ -5,7 +5,7 @@ Index: es2017.object.d.ts
 ===================================================================
 --- es2017.object.d.ts
 +++ es2017.object.d.ts
-@@ -2,34 +2,45 @@
+@@ -2,34 +2,42 @@
    /**
     * Returns an array of values of the enumerable properties of an object
     * @param o Object that contains the properties and methods. This can be an object that you created or an existing Document Object Model (DOM) object.
@@ -23,7 +23,7 @@ Index: es2017.object.d.ts
 +   * Returns an array of values of the enumerable properties of an object
 +   * @param o Object that contains the properties and methods. This can be an object that you created or an existing Document Object Model (DOM) object.
 +   */
-+  values<T>(o: T): CheckNonNullable<T, unknown[]>;
++  values<T>(o: CheckNonNullable<T>): unknown[];
  
    /**
     * Returns an array of key/values of the enumerable properties of an object
@@ -42,7 +42,7 @@ Index: es2017.object.d.ts
 +   * Returns an array of key/values of the enumerable properties of an object
 +   * @param o Object that contains the properties and methods. This can be an object that you created or an existing Document Object Model (DOM) object.
 +   */
-+  entries<T>(o: T): CheckNonNullable<T, [string, unknown][]>;
++  entries<T>(o: CheckNonNullable<T>): [string, unknown][];
  
    /**
     * Returns an object containing all own property descriptors of an object
@@ -52,15 +52,11 @@ Index: es2017.object.d.ts
 -    o: T
 -  ): { [P in keyof T]: TypedPropertyDescriptor<T[P]> } & {
 -    [x: string]: PropertyDescriptor;
--  };
-+  getOwnPropertyDescriptors<T>(o: T): CheckNonNullable<
-+    T,
-+    {
-+      [P in keyof T]: TypedPropertyDescriptor<T[P]>;
-+    } & {
-+      [x: string]: PropertyDescriptor;
-+    }
-+  >;
++  getOwnPropertyDescriptors<T>(o: CheckNonNullable<T>): {
++    [P in keyof T]: TypedPropertyDescriptor<T[P]>;
++  } & {
++    [x: PropertyKey]: PropertyDescriptor;
+   };
  }
 
 ```
diff --git a/docs/diff/es5.d.ts.md b/docs/diff/es5.d.ts.md
index c4643a1..8b2eab6 100644
--- a/docs/diff/es5.d.ts.md
+++ b/docs/diff/es5.d.ts.md
@@ -62,7 +62,7 @@ Index: es5.d.ts
     * @param o The object that references the prototype.
     */
 -  getPrototypeOf(o: any): any;
-+  getPrototypeOf<T>(o: T): CheckNonNullable<T, unknown>;
++  getPrototypeOf<T>(o: CheckNonNullable<T>): unknown;
  
    /**
     * Gets the own property descriptor of the specified object.
@@ -73,10 +73,9 @@ Index: es5.d.ts
 -  getOwnPropertyDescriptor(
 -    o: any,
 +  getOwnPropertyDescriptor<T>(
-+    o: T,
++    o: CheckNonNullable<T>,
      p: PropertyKey
--  ): PropertyDescriptor | undefined;
-+  ): CheckNonNullable<T, PropertyDescriptor | undefined>;
+   ): PropertyDescriptor | undefined;
  
    /**
     * Returns the names of the own properties of an object. The own properties of an object are those that are defined directly
@@ -84,7 +83,7 @@ Index: es5.d.ts
     * @param o Object that contains the own properties.
     */
 -  getOwnPropertyNames(o: any): string[];
-+  getOwnPropertyNames<T>(o: T): CheckNonNullable<T, string[]>;
++  getOwnPropertyNames<T>(o: CheckNonNullable<T>): string[];
  
    /**
     * Creates an object that has the specified prototype or that has null prototype.
@@ -211,12 +210,18 @@ Index: es5.d.ts
    /**
     * Prevents the modification of attributes of existing properties, and prevents the addition of new properties.
     * @param o Object on which to lock the attributes.
-@@ -350,47 +431,19 @@
+@@ -350,47 +431,26 @@
      this: (this: T, ...args: A) => R,
      thisArg: T,
      ...args: A
    ): R;
--
++  /**
++   * For a given function, creates a bound function that has the same body as the original function.
++   * The this object of the bound function is associated with the specified object, and has the specified initial parameters.
++   * @param thisArg The object to be used as the this object.
++   */
++  bind<T>(this: T, thisArg: ThisParameterType<T>): OmitThisParameter<T>;
+ 
    /**
     * For a given function, creates a bound function that has the same body as the original function.
     * The this object of the bound function is associated with the specified object, and has the specified initial parameters.
@@ -263,12 +268,18 @@ Index: es5.d.ts
  
  interface NewableFunction extends Function {
    /**
-@@ -414,51 +467,23 @@
+@@ -414,51 +474,30 @@
      this: new (...args: A) => T,
      thisArg: T,
      ...args: A
    ): void;
--
++  /**
++   * For a given function, creates a bound function that has the same body as the original function.
++   * The this object of the bound function is associated with the specified object, and has the specified initial parameters.
++   * @param thisArg The object to be used as the this object.
++   */
++  bind<T>(this: T, thisArg: any): T;
+ 
    /**
     * For a given function, creates a bound function that has the same body as the original function.
     * The this object of the bound function is associated with the specified object, and has the specified initial parameters.
@@ -320,7 +331,7 @@ Index: es5.d.ts
    callee: Function;
  }
  
-@@ -508,24 +533,28 @@
+@@ -508,24 +547,28 @@
     * Matches a string with a regular expression, and returns an array containing the results of that search.
     * @param regexp A variable name or string literal containing the regular expression pattern and flags.
     */
@@ -353,7 +364,7 @@ Index: es5.d.ts
  
    /**
     * Finds the first substring match in a regular expression search.
-@@ -1187,32 +1216,74 @@
+@@ -1187,32 +1230,74 @@
     * If a member contains nested objects, the nested objects are transformed before the parent object is.
     */
    parse(
@@ -437,7 +448,7 @@ Index: es5.d.ts
  
  /**
   * An intrinsic object that provides functions to convert JavaScript values to and from the JavaScript Object Notation (JSON) format.
-@@ -1276,23 +1347,25 @@
+@@ -1276,23 +1361,25 @@
     * which is coercible to the Boolean value false, or until the end of the array.
     * @param thisArg An object to which the this keyword can refer in the predicate function.
     * If thisArg is omitted, undefined is used as the this value.
@@ -470,7 +481,7 @@ Index: es5.d.ts
    /**
     * Determines whether the specified callback function returns true for any element of an array.
     * @param predicate A function that accepts up to three arguments. The some method calls
-@@ -1300,117 +1373,99 @@
+@@ -1300,117 +1387,99 @@
     * which is coercible to the Boolean value true, or until the end of the array.
     * @param thisArg An object to which the this keyword can refer in the predicate function.
     * If thisArg is omitted, undefined is used as the this value.
@@ -620,7 +631,7 @@ Index: es5.d.ts
      initialValue: U
    ): U;
  
-@@ -1534,23 +1589,25 @@
+@@ -1534,23 +1603,25 @@
     * which is coercible to the Boolean value false, or until the end of the array.
     * @param thisArg An object to which the this keyword can refer in the predicate function.
     * If thisArg is omitted, undefined is used as the this value.
@@ -653,7 +664,7 @@ Index: es5.d.ts
    /**
     * Determines whether the specified callback function returns true for any element of an array.
     * @param predicate A function that accepts up to three arguments. The some method calls
-@@ -1558,133 +1615,113 @@
+@@ -1558,133 +1629,113 @@
     * which is coercible to the Boolean value true, or until the end of the array.
     * @param thisArg An object to which the this keyword can refer in the predicate function.
     * If thisArg is omitted, undefined is used as the this value.
@@ -821,7 +832,7 @@ Index: es5.d.ts
  
  declare var Array: ArrayConstructor;
  
-@@ -1716,9 +1753,15 @@
+@@ -1716,9 +1767,15 @@
  ) => void;
  
  declare type PromiseConstructorLike = new <T>(
@@ -838,7 +849,7 @@ Index: es5.d.ts
    ) => void
  ) => PromiseLike<T>;
  
-@@ -2123,20 +2166,24 @@
+@@ -2123,20 +2180,24 @@
     * is treated as length+end.
     * @param end If not specified, length of the this object is used as its default value.
     */
@@ -867,7 +878,7 @@ Index: es5.d.ts
  
    /**
     * Changes all array elements from `start` to `end` index to a static `value` and returns the modified array
-@@ -2146,21 +2193,24 @@
+@@ -2146,21 +2207,24 @@
     * @param end index to stop filling the array at. If end is negative, it is treated as
     * length+end.
     */
@@ -897,7 +908,7 @@ Index: es5.d.ts
     * Returns the value of the first element in the array where predicate is true, and undefined
     * otherwise.
     * @param predicate find calls predicate once for each element of the array, in ascending
-@@ -2168,13 +2218,12 @@
+@@ -2168,13 +2232,12 @@
     * immediately returns that element value. Otherwise, find returns undefined.
     * @param thisArg If provided, it will be used as the this value for each invocation of
     * predicate. If it is not provided, undefined is used instead.
@@ -914,7 +925,7 @@ Index: es5.d.ts
     * Returns the index of the first element in the array where predicate is true, and -1
     * otherwise.
     * @param predicate find calls predicate once for each element of the array, in ascending
-@@ -2182,23 +2231,22 @@
+@@ -2182,23 +2245,22 @@
     * findIndex immediately returns that element index. Otherwise, findIndex returns -1.
     * @param thisArg If provided, it will be used as the this value for each invocation of
     * predicate. If it is not provided, undefined is used instead.
@@ -944,7 +955,7 @@ Index: es5.d.ts
  
    /**
     * Returns the index of the first occurrence of a value in an array.
-@@ -2226,50 +2274,40 @@
+@@ -2226,50 +2288,40 @@
    /**
     * The length of the array.
     */
@@ -1008,7 +1019,7 @@ Index: es5.d.ts
     * Calls the specified callback function for all the elements in an array. The return value of
     * the callback function is the accumulated result, and is provided as an argument in the next
     * call to the callback function.
-@@ -2278,46 +2316,32 @@
+@@ -2278,46 +2330,32 @@
     * @param initialValue If initialValue is specified, it is used as the initial value to start
     * the accumulation. The first call to the callbackfn function provides this value as an argument
     * instead of an array value.
@@ -1062,7 +1073,7 @@ Index: es5.d.ts
     * Calls the specified callback function for all the elements in an array, in descending order.
     * The return value of the callback function is the accumulated result, and is provided as an
     * argument in the next call to the callback function.
-@@ -2326,14 +2350,14 @@
+@@ -2326,14 +2364,14 @@
     * @param initialValue If initialValue is specified, it is used as the initial value to start
     * the accumulation. The first call to the callbackfn function provides this value as an argument
     * instead of an array value.
@@ -1079,7 +1090,7 @@ Index: es5.d.ts
      initialValue: U
    ): U;
  
-@@ -2354,20 +2378,24 @@
+@@ -2354,20 +2392,24 @@
     * @param start The beginning of the specified portion of the array.
     * @param end The end of the specified portion of the array. This is exclusive of the element at the index 'end'.
     */
@@ -1108,7 +1119,7 @@ Index: es5.d.ts
  
    /**
     * Sorts an array.
-@@ -2422,25 +2450,23 @@
+@@ -2422,25 +2464,23 @@
     * Returns a new array from a set of elements.
     * @param items A set of elements to include in the new array object.
     */
@@ -1141,7 +1152,7 @@ Index: es5.d.ts
  }
  declare var Int8Array: Int8ArrayConstructor;
  
-@@ -2478,20 +2504,24 @@
+@@ -2478,20 +2518,24 @@
     * is treated as length+end.
     * @param end If not specified, length of the this object is used as its default value.
     */
@@ -1170,7 +1181,7 @@ Index: es5.d.ts
  
    /**
     * Changes all array elements from `start` to `end` index to a static `value` and returns the modified array
-@@ -2501,21 +2531,24 @@
+@@ -2501,21 +2545,24 @@
     * @param end index to stop filling the array at. If end is negative, it is treated as
     * length+end.
     */
@@ -1200,7 +1211,7 @@ Index: es5.d.ts
     * Returns the value of the first element in the array where predicate is true, and undefined
     * otherwise.
     * @param predicate find calls predicate once for each element of the array, in ascending
-@@ -2523,13 +2556,12 @@
+@@ -2523,13 +2570,12 @@
     * immediately returns that element value. Otherwise, find returns undefined.
     * @param thisArg If provided, it will be used as the this value for each invocation of
     * predicate. If it is not provided, undefined is used instead.
@@ -1217,7 +1228,7 @@ Index: es5.d.ts
     * Returns the index of the first element in the array where predicate is true, and -1
     * otherwise.
     * @param predicate find calls predicate once for each element of the array, in ascending
-@@ -2537,23 +2569,22 @@
+@@ -2537,23 +2583,22 @@
     * findIndex immediately returns that element index. Otherwise, findIndex returns -1.
     * @param thisArg If provided, it will be used as the this value for each invocation of
     * predicate. If it is not provided, undefined is used instead.
@@ -1247,7 +1258,7 @@ Index: es5.d.ts
  
    /**
     * Returns the index of the first occurrence of a value in an array.
-@@ -2581,50 +2612,40 @@
+@@ -2581,50 +2626,40 @@
    /**
     * The length of the array.
     */
@@ -1311,7 +1322,7 @@ Index: es5.d.ts
     * Calls the specified callback function for all the elements in an array. The return value of
     * the callback function is the accumulated result, and is provided as an argument in the next
     * call to the callback function.
-@@ -2633,46 +2654,32 @@
+@@ -2633,46 +2668,32 @@
     * @param initialValue If initialValue is specified, it is used as the initial value to start
     * the accumulation. The first call to the callbackfn function provides this value as an argument
     * instead of an array value.
@@ -1365,7 +1376,7 @@ Index: es5.d.ts
     * Calls the specified callback function for all the elements in an array, in descending order.
     * The return value of the callback function is the accumulated result, and is provided as an
     * argument in the next call to the callback function.
-@@ -2681,14 +2688,14 @@
+@@ -2681,14 +2702,14 @@
     * @param initialValue If initialValue is specified, it is used as the initial value to start
     * the accumulation. The first call to the callbackfn function provides this value as an argument
     * instead of an array value.
@@ -1382,7 +1393,7 @@ Index: es5.d.ts
      initialValue: U
    ): U;
  
-@@ -2709,20 +2716,24 @@
+@@ -2709,20 +2730,24 @@
     * @param start The beginning of the specified portion of the array.
     * @param end The end of the specified portion of the array. This is exclusive of the element at the index 'end'.
     */
@@ -1411,7 +1422,7 @@ Index: es5.d.ts
  
    /**
     * Sorts an array.
-@@ -2778,25 +2789,23 @@
+@@ -2778,25 +2803,23 @@
     * Returns a new array from a set of elements.
     * @param items A set of elements to include in the new array object.
     */
@@ -1444,7 +1455,7 @@ Index: es5.d.ts
  }
  declare var Uint8Array: Uint8ArrayConstructor;
  
-@@ -2834,24 +2843,24 @@
+@@ -2834,24 +2857,24 @@
     * is treated as length+end.
     * @param end If not specified, length of the this object is used as its default value.
     */
@@ -1474,7 +1485,7 @@ Index: es5.d.ts
  
    /**
     * Changes all array elements from `start` to `end` index to a static `value` and returns the modified array
-@@ -2861,21 +2870,24 @@
+@@ -2861,21 +2884,24 @@
     * @param end index to stop filling the array at. If end is negative, it is treated as
     * length+end.
     */
@@ -1504,7 +1515,7 @@ Index: es5.d.ts
     * Returns the value of the first element in the array where predicate is true, and undefined
     * otherwise.
     * @param predicate find calls predicate once for each element of the array, in ascending
-@@ -2883,17 +2895,12 @@
+@@ -2883,17 +2909,12 @@
     * immediately returns that element value. Otherwise, find returns undefined.
     * @param thisArg If provided, it will be used as the this value for each invocation of
     * predicate. If it is not provided, undefined is used instead.
@@ -1525,7 +1536,7 @@ Index: es5.d.ts
     * Returns the index of the first element in the array where predicate is true, and -1
     * otherwise.
     * @param predicate find calls predicate once for each element of the array, in ascending
-@@ -2901,31 +2908,22 @@
+@@ -2901,31 +2922,22 @@
     * findIndex immediately returns that element index. Otherwise, findIndex returns -1.
     * @param thisArg If provided, it will be used as the this value for each invocation of
     * predicate. If it is not provided, undefined is used instead.
@@ -1563,7 +1574,7 @@ Index: es5.d.ts
  
    /**
     * Returns the index of the first occurrence of a value in an array.
-@@ -2953,54 +2951,40 @@
+@@ -2953,54 +2965,40 @@
    /**
     * The length of the array.
     */
@@ -1627,7 +1638,7 @@ Index: es5.d.ts
     * Calls the specified callback function for all the elements in an array. The return value of
     * the callback function is the accumulated result, and is provided as an argument in the next
     * call to the callback function.
-@@ -3009,46 +2993,32 @@
+@@ -3009,46 +3007,32 @@
     * @param initialValue If initialValue is specified, it is used as the initial value to start
     * the accumulation. The first call to the callbackfn function provides this value as an argument
     * instead of an array value.
@@ -1681,7 +1692,7 @@ Index: es5.d.ts
     * Calls the specified callback function for all the elements in an array, in descending order.
     * The return value of the callback function is the accumulated result, and is provided as an
     * argument in the next call to the callback function.
-@@ -3057,14 +3027,14 @@
+@@ -3057,14 +3041,14 @@
     * @param initialValue If initialValue is specified, it is used as the initial value to start
     * the accumulation. The first call to the callbackfn function provides this value as an argument
     * instead of an array value.
@@ -1698,7 +1709,7 @@ Index: es5.d.ts
      initialValue: U
    ): U;
  
-@@ -3085,24 +3055,24 @@
+@@ -3085,24 +3069,24 @@
     * @param start The beginning of the specified portion of the array.
     * @param end The end of the specified portion of the array. This is exclusive of the element at the index 'end'.
     */
@@ -1728,7 +1739,7 @@ Index: es5.d.ts
  
    /**
     * Sorts an array.
-@@ -3158,25 +3128,23 @@
+@@ -3158,25 +3142,23 @@
     * Returns a new array from a set of elements.
     * @param items A set of elements to include in the new array object.
     */
@@ -1761,7 +1772,7 @@ Index: es5.d.ts
  }
  declare var Uint8ClampedArray: Uint8ClampedArrayConstructor;
  
-@@ -3214,20 +3182,24 @@
+@@ -3214,20 +3196,24 @@
     * is treated as length+end.
     * @param end If not specified, length of the this object is used as its default value.
     */
@@ -1790,7 +1801,7 @@ Index: es5.d.ts
  
    /**
     * Changes all array elements from `start` to `end` index to a static `value` and returns the modified array
-@@ -3237,21 +3209,24 @@
+@@ -3237,21 +3223,24 @@
     * @param end index to stop filling the array at. If end is negative, it is treated as
     * length+end.
     */
@@ -1820,7 +1831,7 @@ Index: es5.d.ts
     * Returns the value of the first element in the array where predicate is true, and undefined
     * otherwise.
     * @param predicate find calls predicate once for each element of the array, in ascending
-@@ -3259,13 +3234,12 @@
+@@ -3259,13 +3248,12 @@
     * immediately returns that element value. Otherwise, find returns undefined.
     * @param thisArg If provided, it will be used as the this value for each invocation of
     * predicate. If it is not provided, undefined is used instead.
@@ -1837,7 +1848,7 @@ Index: es5.d.ts
     * Returns the index of the first element in the array where predicate is true, and -1
     * otherwise.
     * @param predicate find calls predicate once for each element of the array, in ascending
-@@ -3273,23 +3247,22 @@
+@@ -3273,23 +3261,22 @@
     * findIndex immediately returns that element index. Otherwise, findIndex returns -1.
     * @param thisArg If provided, it will be used as the this value for each invocation of
     * predicate. If it is not provided, undefined is used instead.
@@ -1867,7 +1878,7 @@ Index: es5.d.ts
    /**
     * Returns the index of the first occurrence of a value in an array.
     * @param searchElement The value to locate in the array.
-@@ -3316,50 +3289,40 @@
+@@ -3316,50 +3303,40 @@
    /**
     * The length of the array.
     */
@@ -1931,7 +1942,7 @@ Index: es5.d.ts
     * Calls the specified callback function for all the elements in an array. The return value of
     * the callback function is the accumulated result, and is provided as an argument in the next
     * call to the callback function.
-@@ -3368,46 +3331,32 @@
+@@ -3368,46 +3345,32 @@
     * @param initialValue If initialValue is specified, it is used as the initial value to start
     * the accumulation. The first call to the callbackfn function provides this value as an argument
     * instead of an array value.
@@ -1985,7 +1996,7 @@ Index: es5.d.ts
     * Calls the specified callback function for all the elements in an array, in descending order.
     * The return value of the callback function is the accumulated result, and is provided as an
     * argument in the next call to the callback function.
-@@ -3416,14 +3365,14 @@
+@@ -3416,14 +3379,14 @@
     * @param initialValue If initialValue is specified, it is used as the initial value to start
     * the accumulation. The first call to the callbackfn function provides this value as an argument
     * instead of an array value.
@@ -2002,7 +2013,7 @@ Index: es5.d.ts
      initialValue: U
    ): U;
  
-@@ -3444,20 +3393,24 @@
+@@ -3444,20 +3407,24 @@
     * @param start The beginning of the specified portion of the array.
     * @param end The end of the specified portion of the array. This is exclusive of the element at the index 'end'.
     */
@@ -2031,7 +2042,7 @@ Index: es5.d.ts
  
    /**
     * Sorts an array.
-@@ -3513,25 +3466,23 @@
+@@ -3513,25 +3480,23 @@
     * Returns a new array from a set of elements.
     * @param items A set of elements to include in the new array object.
     */
@@ -2064,7 +2075,7 @@ Index: es5.d.ts
  }
  declare var Int16Array: Int16ArrayConstructor;
  
-@@ -3569,20 +3520,24 @@
+@@ -3569,20 +3534,24 @@
     * is treated as length+end.
     * @param end If not specified, length of the this object is used as its default value.
     */
@@ -2093,7 +2104,7 @@ Index: es5.d.ts
  
    /**
     * Changes all array elements from `start` to `end` index to a static `value` and returns the modified array
-@@ -3592,21 +3547,24 @@
+@@ -3592,21 +3561,24 @@
     * @param end index to stop filling the array at. If end is negative, it is treated as
     * length+end.
     */
@@ -2123,7 +2134,7 @@ Index: es5.d.ts
     * Returns the value of the first element in the array where predicate is true, and undefined
     * otherwise.
     * @param predicate find calls predicate once for each element of the array, in ascending
-@@ -3614,13 +3572,12 @@
+@@ -3614,13 +3586,12 @@
     * immediately returns that element value. Otherwise, find returns undefined.
     * @param thisArg If provided, it will be used as the this value for each invocation of
     * predicate. If it is not provided, undefined is used instead.
@@ -2140,7 +2151,7 @@ Index: es5.d.ts
     * Returns the index of the first element in the array where predicate is true, and -1
     * otherwise.
     * @param predicate find calls predicate once for each element of the array, in ascending
-@@ -3628,23 +3585,22 @@
+@@ -3628,23 +3599,22 @@
     * findIndex immediately returns that element index. Otherwise, findIndex returns -1.
     * @param thisArg If provided, it will be used as the this value for each invocation of
     * predicate. If it is not provided, undefined is used instead.
@@ -2170,7 +2181,7 @@ Index: es5.d.ts
  
    /**
     * Returns the index of the first occurrence of a value in an array.
-@@ -3672,50 +3628,40 @@
+@@ -3672,50 +3642,40 @@
    /**
     * The length of the array.
     */
@@ -2234,7 +2245,7 @@ Index: es5.d.ts
     * Calls the specified callback function for all the elements in an array. The return value of
     * the callback function is the accumulated result, and is provided as an argument in the next
     * call to the callback function.
-@@ -3724,46 +3670,32 @@
+@@ -3724,46 +3684,32 @@
     * @param initialValue If initialValue is specified, it is used as the initial value to start
     * the accumulation. The first call to the callbackfn function provides this value as an argument
     * instead of an array value.
@@ -2288,7 +2299,7 @@ Index: es5.d.ts
     * Calls the specified callback function for all the elements in an array, in descending order.
     * The return value of the callback function is the accumulated result, and is provided as an
     * argument in the next call to the callback function.
-@@ -3772,14 +3704,14 @@
+@@ -3772,14 +3718,14 @@
     * @param initialValue If initialValue is specified, it is used as the initial value to start
     * the accumulation. The first call to the callbackfn function provides this value as an argument
     * instead of an array value.
@@ -2305,7 +2316,7 @@ Index: es5.d.ts
      initialValue: U
    ): U;
  
-@@ -3800,20 +3732,24 @@
+@@ -3800,20 +3746,24 @@
     * @param start The beginning of the specified portion of the array.
     * @param end The end of the specified portion of the array. This is exclusive of the element at the index 'end'.
     */
@@ -2334,7 +2345,7 @@ Index: es5.d.ts
  
    /**
     * Sorts an array.
-@@ -3869,25 +3805,23 @@
+@@ -3869,25 +3819,23 @@
     * Returns a new array from a set of elements.
     * @param items A set of elements to include in the new array object.
     */
@@ -2367,7 +2378,7 @@ Index: es5.d.ts
  }
  declare var Uint16Array: Uint16ArrayConstructor;
  /**
-@@ -3924,20 +3858,24 @@
+@@ -3924,20 +3872,24 @@
     * is treated as length+end.
     * @param end If not specified, length of the this object is used as its default value.
     */
@@ -2396,7 +2407,7 @@ Index: es5.d.ts
  
    /**
     * Changes all array elements from `start` to `end` index to a static `value` and returns the modified array
-@@ -3947,21 +3885,24 @@
+@@ -3947,21 +3899,24 @@
     * @param end index to stop filling the array at. If end is negative, it is treated as
     * length+end.
     */
@@ -2426,7 +2437,7 @@ Index: es5.d.ts
     * Returns the value of the first element in the array where predicate is true, and undefined
     * otherwise.
     * @param predicate find calls predicate once for each element of the array, in ascending
-@@ -3969,13 +3910,12 @@
+@@ -3969,13 +3924,12 @@
     * immediately returns that element value. Otherwise, find returns undefined.
     * @param thisArg If provided, it will be used as the this value for each invocation of
     * predicate. If it is not provided, undefined is used instead.
@@ -2443,7 +2454,7 @@ Index: es5.d.ts
     * Returns the index of the first element in the array where predicate is true, and -1
     * otherwise.
     * @param predicate find calls predicate once for each element of the array, in ascending
-@@ -3983,23 +3923,22 @@
+@@ -3983,23 +3937,22 @@
     * findIndex immediately returns that element index. Otherwise, findIndex returns -1.
     * @param thisArg If provided, it will be used as the this value for each invocation of
     * predicate. If it is not provided, undefined is used instead.
@@ -2473,7 +2484,7 @@ Index: es5.d.ts
  
    /**
     * Returns the index of the first occurrence of a value in an array.
-@@ -4027,50 +3966,40 @@
+@@ -4027,50 +3980,40 @@
    /**
     * The length of the array.
     */
@@ -2537,7 +2548,7 @@ Index: es5.d.ts
     * Calls the specified callback function for all the elements in an array. The return value of
     * the callback function is the accumulated result, and is provided as an argument in the next
     * call to the callback function.
-@@ -4079,46 +4008,32 @@
+@@ -4079,46 +4022,32 @@
     * @param initialValue If initialValue is specified, it is used as the initial value to start
     * the accumulation. The first call to the callbackfn function provides this value as an argument
     * instead of an array value.
@@ -2591,7 +2602,7 @@ Index: es5.d.ts
     * Calls the specified callback function for all the elements in an array, in descending order.
     * The return value of the callback function is the accumulated result, and is provided as an
     * argument in the next call to the callback function.
-@@ -4127,14 +4042,14 @@
+@@ -4127,14 +4056,14 @@
     * @param initialValue If initialValue is specified, it is used as the initial value to start
     * the accumulation. The first call to the callbackfn function provides this value as an argument
     * instead of an array value.
@@ -2608,7 +2619,7 @@ Index: es5.d.ts
      initialValue: U
    ): U;
  
-@@ -4155,20 +4070,24 @@
+@@ -4155,20 +4084,24 @@
     * @param start The beginning of the specified portion of the array.
     * @param end The end of the specified portion of the array. This is exclusive of the element at the index 'end'.
     */
@@ -2637,7 +2648,7 @@ Index: es5.d.ts
  
    /**
     * Sorts an array.
-@@ -4224,25 +4143,23 @@
+@@ -4224,25 +4157,23 @@
     * Returns a new array from a set of elements.
     * @param items A set of elements to include in the new array object.
     */
@@ -2670,7 +2681,7 @@ Index: es5.d.ts
  }
  declare var Int32Array: Int32ArrayConstructor;
  
-@@ -4280,20 +4197,24 @@
+@@ -4280,20 +4211,24 @@
     * is treated as length+end.
     * @param end If not specified, length of the this object is used as its default value.
     */
@@ -2699,7 +2710,7 @@ Index: es5.d.ts
  
    /**
     * Changes all array elements from `start` to `end` index to a static `value` and returns the modified array
-@@ -4303,21 +4224,24 @@
+@@ -4303,21 +4238,24 @@
     * @param end index to stop filling the array at. If end is negative, it is treated as
     * length+end.
     */
@@ -2729,7 +2740,7 @@ Index: es5.d.ts
     * Returns the value of the first element in the array where predicate is true, and undefined
     * otherwise.
     * @param predicate find calls predicate once for each element of the array, in ascending
-@@ -4325,13 +4249,12 @@
+@@ -4325,13 +4263,12 @@
     * immediately returns that element value. Otherwise, find returns undefined.
     * @param thisArg If provided, it will be used as the this value for each invocation of
     * predicate. If it is not provided, undefined is used instead.
@@ -2746,7 +2757,7 @@ Index: es5.d.ts
     * Returns the index of the first element in the array where predicate is true, and -1
     * otherwise.
     * @param predicate find calls predicate once for each element of the array, in ascending
-@@ -4339,23 +4262,22 @@
+@@ -4339,23 +4276,22 @@
     * findIndex immediately returns that element index. Otherwise, findIndex returns -1.
     * @param thisArg If provided, it will be used as the this value for each invocation of
     * predicate. If it is not provided, undefined is used instead.
@@ -2776,7 +2787,7 @@ Index: es5.d.ts
    /**
     * Returns the index of the first occurrence of a value in an array.
     * @param searchElement The value to locate in the array.
-@@ -4382,50 +4304,40 @@
+@@ -4382,50 +4318,40 @@
    /**
     * The length of the array.
     */
@@ -2840,7 +2851,7 @@ Index: es5.d.ts
     * Calls the specified callback function for all the elements in an array. The return value of
     * the callback function is the accumulated result, and is provided as an argument in the next
     * call to the callback function.
-@@ -4434,46 +4346,32 @@
+@@ -4434,46 +4360,32 @@
     * @param initialValue If initialValue is specified, it is used as the initial value to start
     * the accumulation. The first call to the callbackfn function provides this value as an argument
     * instead of an array value.
@@ -2894,7 +2905,7 @@ Index: es5.d.ts
     * Calls the specified callback function for all the elements in an array, in descending order.
     * The return value of the callback function is the accumulated result, and is provided as an
     * argument in the next call to the callback function.
-@@ -4482,14 +4380,14 @@
+@@ -4482,14 +4394,14 @@
     * @param initialValue If initialValue is specified, it is used as the initial value to start
     * the accumulation. The first call to the callbackfn function provides this value as an argument
     * instead of an array value.
@@ -2911,7 +2922,7 @@ Index: es5.d.ts
      initialValue: U
    ): U;
  
-@@ -4510,20 +4408,24 @@
+@@ -4510,20 +4422,24 @@
     * @param start The beginning of the specified portion of the array.
     * @param end The end of the specified portion of the array. This is exclusive of the element at the index 'end'.
     */
@@ -2940,7 +2951,7 @@ Index: es5.d.ts
  
    /**
     * Sorts an array.
-@@ -4579,25 +4481,23 @@
+@@ -4579,25 +4495,23 @@
     * Returns a new array from a set of elements.
     * @param items A set of elements to include in the new array object.
     */
@@ -2973,7 +2984,7 @@ Index: es5.d.ts
  }
  declare var Uint32Array: Uint32ArrayConstructor;
  
-@@ -4635,20 +4535,24 @@
+@@ -4635,20 +4549,24 @@
     * is treated as length+end.
     * @param end If not specified, length of the this object is used as its default value.
     */
@@ -3002,7 +3013,7 @@ Index: es5.d.ts
  
    /**
     * Changes all array elements from `start` to `end` index to a static `value` and returns the modified array
-@@ -4658,21 +4562,24 @@
+@@ -4658,21 +4576,24 @@
     * @param end index to stop filling the array at. If end is negative, it is treated as
     * length+end.
     */
@@ -3032,7 +3043,7 @@ Index: es5.d.ts
     * Returns the value of the first element in the array where predicate is true, and undefined
     * otherwise.
     * @param predicate find calls predicate once for each element of the array, in ascending
-@@ -4680,13 +4587,12 @@
+@@ -4680,13 +4601,12 @@
     * immediately returns that element value. Otherwise, find returns undefined.
     * @param thisArg If provided, it will be used as the this value for each invocation of
     * predicate. If it is not provided, undefined is used instead.
@@ -3049,7 +3060,7 @@ Index: es5.d.ts
     * Returns the index of the first element in the array where predicate is true, and -1
     * otherwise.
     * @param predicate find calls predicate once for each element of the array, in ascending
-@@ -4694,23 +4600,22 @@
+@@ -4694,23 +4614,22 @@
     * findIndex immediately returns that element index. Otherwise, findIndex returns -1.
     * @param thisArg If provided, it will be used as the this value for each invocation of
     * predicate. If it is not provided, undefined is used instead.
@@ -3079,7 +3090,7 @@ Index: es5.d.ts
  
    /**
     * Returns the index of the first occurrence of a value in an array.
-@@ -4738,50 +4643,40 @@
+@@ -4738,50 +4657,40 @@
    /**
     * The length of the array.
     */
@@ -3143,7 +3154,7 @@ Index: es5.d.ts
     * Calls the specified callback function for all the elements in an array. The return value of
     * the callback function is the accumulated result, and is provided as an argument in the next
     * call to the callback function.
-@@ -4790,46 +4685,32 @@
+@@ -4790,46 +4699,32 @@
     * @param initialValue If initialValue is specified, it is used as the initial value to start
     * the accumulation. The first call to the callbackfn function provides this value as an argument
     * instead of an array value.
@@ -3197,7 +3208,7 @@ Index: es5.d.ts
     * Calls the specified callback function for all the elements in an array, in descending order.
     * The return value of the callback function is the accumulated result, and is provided as an
     * argument in the next call to the callback function.
-@@ -4838,14 +4719,14 @@
+@@ -4838,14 +4733,14 @@
     * @param initialValue If initialValue is specified, it is used as the initial value to start
     * the accumulation. The first call to the callbackfn function provides this value as an argument
     * instead of an array value.
@@ -3214,7 +3225,7 @@ Index: es5.d.ts
      initialValue: U
    ): U;
  
-@@ -4866,20 +4747,24 @@
+@@ -4866,20 +4761,24 @@
     * @param start The beginning of the specified portion of the array.
     * @param end The end of the specified portion of the array. This is exclusive of the element at the index 'end'.
     */
@@ -3243,7 +3254,7 @@ Index: es5.d.ts
  
    /**
     * Sorts an array.
-@@ -4935,25 +4820,23 @@
+@@ -4935,25 +4834,23 @@
     * Returns a new array from a set of elements.
     * @param items A set of elements to include in the new array object.
     */
@@ -3276,7 +3287,7 @@ Index: es5.d.ts
  }
  declare var Float32Array: Float32ArrayConstructor;
  
-@@ -4991,20 +4874,24 @@
+@@ -4991,20 +4888,24 @@
     * is treated as length+end.
     * @param end If not specified, length of the this object is used as its default value.
     */
@@ -3305,7 +3316,7 @@ Index: es5.d.ts
  
    /**
     * Changes all array elements from `start` to `end` index to a static `value` and returns the modified array
-@@ -5014,21 +4901,24 @@
+@@ -5014,21 +4915,24 @@
     * @param end index to stop filling the array at. If end is negative, it is treated as
     * length+end.
     */
@@ -3335,7 +3346,7 @@ Index: es5.d.ts
     * Returns the value of the first element in the array where predicate is true, and undefined
     * otherwise.
     * @param predicate find calls predicate once for each element of the array, in ascending
-@@ -5036,13 +4926,12 @@
+@@ -5036,13 +4940,12 @@
     * immediately returns that element value. Otherwise, find returns undefined.
     * @param thisArg If provided, it will be used as the this value for each invocation of
     * predicate. If it is not provided, undefined is used instead.
@@ -3352,7 +3363,7 @@ Index: es5.d.ts
     * Returns the index of the first element in the array where predicate is true, and -1
     * otherwise.
     * @param predicate find calls predicate once for each element of the array, in ascending
-@@ -5050,23 +4939,22 @@
+@@ -5050,23 +4953,22 @@
     * findIndex immediately returns that element index. Otherwise, findIndex returns -1.
     * @param thisArg If provided, it will be used as the this value for each invocation of
     * predicate. If it is not provided, undefined is used instead.
@@ -3382,7 +3393,7 @@ Index: es5.d.ts
  
    /**
     * Returns the index of the first occurrence of a value in an array.
-@@ -5094,50 +4982,40 @@
+@@ -5094,50 +4996,40 @@
    /**
     * The length of the array.
     */
@@ -3446,7 +3457,7 @@ Index: es5.d.ts
     * Calls the specified callback function for all the elements in an array. The return value of
     * the callback function is the accumulated result, and is provided as an argument in the next
     * call to the callback function.
-@@ -5146,46 +5024,32 @@
+@@ -5146,46 +5038,32 @@
     * @param initialValue If initialValue is specified, it is used as the initial value to start
     * the accumulation. The first call to the callbackfn function provides this value as an argument
     * instead of an array value.
@@ -3500,7 +3511,7 @@ Index: es5.d.ts
     * Calls the specified callback function for all the elements in an array, in descending order.
     * The return value of the callback function is the accumulated result, and is provided as an
     * argument in the next call to the callback function.
-@@ -5194,14 +5058,14 @@
+@@ -5194,14 +5072,14 @@
     * @param initialValue If initialValue is specified, it is used as the initial value to start
     * the accumulation. The first call to the callbackfn function provides this value as an argument
     * instead of an array value.
@@ -3517,7 +3528,7 @@ Index: es5.d.ts
      initialValue: U
    ): U;
  
-@@ -5222,20 +5086,24 @@
+@@ -5222,20 +5100,24 @@
     * @param start The beginning of the specified portion of the array.
     * @param end The end of the specified portion of the array. This is exclusive of the element at the index 'end'.
     */
@@ -3546,7 +3557,7 @@ Index: es5.d.ts
  
    /**
     * Sorts an array.
-@@ -5282,25 +5150,23 @@
+@@ -5282,25 +5164,23 @@
     * Returns a new array from a set of elements.
     * @param items A set of elements to include in the new array object.
     */
@@ -3579,21 +3590,28 @@ Index: es5.d.ts
  }
  declare var Float64Array: Float64ArrayConstructor;
  
-@@ -5491,4 +5357,24 @@
+@@ -5491,4 +5371,31 @@
      locales?: string | string[],
      options?: Intl.DateTimeFormatOptions
    ): string;
  }
 +// --------------------
-+type First<T> = T extends [any] ? T[0] : unknown;
++type Cast<T, U> = T extends U ? T : U;
++
++/**
++ * Make all properties in T writable
++ */
++type Writable<T> = {
++  -readonly [P in keyof T]: T[P];
++};
 +
-+type UnionToIntersection<T> = (
-+  T extends any ? (arg: T) => void : never
-+) extends (arg: infer F) => void
-+  ? F
-+  : unknown;
++type Intersect<T extends readonly any[]> = ((
++  ...args: { [K in keyof T]: Cast<Writable<T[K]>, {}> }
++) => void) extends (...args: { [K in keyof T]: infer S }) => void
++  ? S
++  : never;
 +
-+type CheckNonNullable<T, U> = [T] extends [NonNullable<T>] ? U : never;
++type CheckNonNullable<T> = [T] extends [null | undefined] ? never : T;
 +
 +type JSONValue =
 +  | null
diff --git a/generated/lib.es2015.core.d.ts b/generated/lib.es2015.core.d.ts
index 1a7c668..9226425 100644
--- a/generated/lib.es2015.core.d.ts
+++ b/generated/lib.es2015.core.d.ts
@@ -343,25 +343,15 @@ interface ObjectConstructor {
    * @param sources One or more source objects from which to copy properties
    */
   assign<T, Ts extends readonly any[]>(
-    target: T,
+    target: CheckNonNullable<T>,
     ...sources: Ts
-  ): CheckNonNullable<
-    T,
-    First<
-      UnionToIntersection<
-        | [T]
-        | {
-            [K in keyof Ts]: [Ts[K]];
-          }[number]
-      >
-    >
-  >;
+  ): Intersect<[T, ...Ts]>;
 
   /**
    * Returns an array of all symbol properties found directly on object o.
    * @param o Object to retrieve the symbols from.
    */
-  getOwnPropertySymbols(o: any): symbol[];
+  getOwnPropertySymbols<T>(o: CheckNonNullable<T>): symbol[];
 
   /**
    * Returns the names of the enumerable string properties and methods of an object.
@@ -422,6 +412,11 @@ interface ObjectConstructor {
 //      */
 //     assign(target: object, ...sources: any[]): any;
 //     /**
+//      * Returns an array of all symbol properties found directly on object o.
+//      * @param o Object to retrieve the symbols from.
+//      */
+//     getOwnPropertySymbols(o: any): symbol[];
+//     /**
 //      * Returns true if the values are the same value, false otherwise.
 //      * @param value1 The first value.
 //      * @param value2 The second value.
diff --git a/generated/lib.es2017.object.d.ts b/generated/lib.es2017.object.d.ts
index 7ea448f..3e3845a 100644
--- a/generated/lib.es2017.object.d.ts
+++ b/generated/lib.es2017.object.d.ts
@@ -13,7 +13,7 @@ interface ObjectConstructor {
    * Returns an array of values of the enumerable properties of an object
    * @param o Object that contains the properties and methods. This can be an object that you created or an existing Document Object Model (DOM) object.
    */
-  values<T>(o: T): CheckNonNullable<T, unknown[]>;
+  values<T>(o: CheckNonNullable<T>): unknown[];
 
   /**
    * Returns an array of key/values of the enumerable properties of an object
@@ -29,20 +29,17 @@ interface ObjectConstructor {
    * Returns an array of key/values of the enumerable properties of an object
    * @param o Object that contains the properties and methods. This can be an object that you created or an existing Document Object Model (DOM) object.
    */
-  entries<T>(o: T): CheckNonNullable<T, [string, unknown][]>;
+  entries<T>(o: CheckNonNullable<T>): [string, unknown][];
 
   /**
    * Returns an object containing all own property descriptors of an object
    * @param o Object that contains the properties and methods. This can be an object that you created or an existing Document Object Model (DOM) object.
    */
-  getOwnPropertyDescriptors<T>(o: T): CheckNonNullable<
-    T,
-    {
-      [P in keyof T]: TypedPropertyDescriptor<T[P]>;
-    } & {
-      [x: string]: PropertyDescriptor;
-    }
-  >;
+  getOwnPropertyDescriptors<T>(o: CheckNonNullable<T>): {
+    [P in keyof T]: TypedPropertyDescriptor<T[P]>;
+  } & {
+    [x: PropertyKey]: PropertyDescriptor;
+  };
 }
 //     /**
 //      * Returns an array of values of the enumerable properties of an object
diff --git a/generated/lib.es5.d.ts b/generated/lib.es5.d.ts
index b92c308..fc95925 100644
--- a/generated/lib.es5.d.ts
+++ b/generated/lib.es5.d.ts
@@ -166,7 +166,7 @@ interface ObjectConstructor {
    * Returns the prototype of an object.
    * @param o The object that references the prototype.
    */
-  getPrototypeOf<T>(o: T): CheckNonNullable<T, unknown>;
+  getPrototypeOf<T>(o: CheckNonNullable<T>): unknown;
 
   /**
    * Gets the own property descriptor of the specified object.
@@ -175,16 +175,16 @@ interface ObjectConstructor {
    * @param p Name of the property.
    */
   getOwnPropertyDescriptor<T>(
-    o: T,
+    o: CheckNonNullable<T>,
     p: PropertyKey
-  ): CheckNonNullable<T, PropertyDescriptor | undefined>;
+  ): PropertyDescriptor | undefined;
 
   /**
    * Returns the names of the own properties of an object. The own properties of an object are those that are defined directly
    * on that object, and are not inherited from the object's prototype. The properties of an object include both fields (objects) and functions.
    * @param o Object that contains the own properties.
    */
-  getOwnPropertyNames<T>(o: T): CheckNonNullable<T, string[]>;
+  getOwnPropertyNames<T>(o: CheckNonNullable<T>): string[];
 
   /**
    * Creates an object that has the specified prototype or that has null prototype.
@@ -487,6 +487,13 @@ interface CallableFunction extends Function {
     thisArg: T,
     ...args: A
   ): R;
+  /**
+   * For a given function, creates a bound function that has the same body as the original function.
+   * The this object of the bound function is associated with the specified object, and has the specified initial parameters.
+   * @param thisArg The object to be used as the this object.
+   */
+  bind<T>(this: T, thisArg: ThisParameterType<T>): OmitThisParameter<T>;
+
   /**
    * For a given function, creates a bound function that has the same body as the original function.
    * The this object of the bound function is associated with the specified object, and has the specified initial parameters.
@@ -535,6 +542,13 @@ interface NewableFunction extends Function {
     thisArg: T,
     ...args: A
   ): void;
+  /**
+   * For a given function, creates a bound function that has the same body as the original function.
+   * The this object of the bound function is associated with the specified object, and has the specified initial parameters.
+   * @param thisArg The object to be used as the this object.
+   */
+  bind<T>(this: T, thisArg: any): T;
+
   /**
    * For a given function, creates a bound function that has the same body as the original function.
    * The this object of the bound function is associated with the specified object, and has the specified initial parameters.
@@ -6734,15 +6748,22 @@ interface Date {
   ): string;
 }
 // --------------------
-type First<T> = T extends [any] ? T[0] : unknown;
+type Cast<T, U> = T extends U ? T : U;
 
-type UnionToIntersection<T> = (
-  T extends any ? (arg: T) => void : never
-) extends (arg: infer F) => void
-  ? F
-  : unknown;
+/**
+ * Make all properties in T writable
+ */
+type Writable<T> = {
+  -readonly [P in keyof T]: T[P];
+};
+
+type Intersect<T extends readonly any[]> = ((
+  ...args: { [K in keyof T]: Cast<Writable<T[K]>, {}> }
+) => void) extends (...args: { [K in keyof T]: infer S }) => void
+  ? S
+  : never;
 
-type CheckNonNullable<T, U> = [T] extends [NonNullable<T>] ? U : never;
+type CheckNonNullable<T> = [T] extends [null | undefined] ? never : T;
 
 type JSONValue =
   | null
diff --git a/lib/lib.es2015.core.d.ts b/lib/lib.es2015.core.d.ts
index 98855ab..5cf8d74 100644
--- a/lib/lib.es2015.core.d.ts
+++ b/lib/lib.es2015.core.d.ts
@@ -100,12 +100,15 @@ interface ObjectConstructor {
    * @param sources One or more source objects from which to copy properties
    */
   assign<T, Ts extends readonly any[]>(
-    target: T,
+    target: CheckNonNullable<T>,
     ...sources: Ts
-  ): CheckNonNullable<
-    T,
-    First<UnionToIntersection<[T] | { [K in keyof Ts]: [Ts[K]] }[number]>>
-  >;
+  ): Intersect<[T, ...Ts]>;
+
+  /**
+   * Returns an array of all symbol properties found directly on object o.
+   * @param o Object to retrieve the symbols from.
+   */
+  getOwnPropertySymbols<T>(o: CheckNonNullable<T>): symbol[];
 
   /**
    * Returns true if the values are the same value, false otherwise.
diff --git a/lib/lib.es2017.object.d.ts b/lib/lib.es2017.object.d.ts
index 9de9db4..49c1405 100644
--- a/lib/lib.es2017.object.d.ts
+++ b/lib/lib.es2017.object.d.ts
@@ -13,7 +13,7 @@ interface ObjectConstructor {
    * Returns an array of values of the enumerable properties of an object
    * @param o Object that contains the properties and methods. This can be an object that you created or an existing Document Object Model (DOM) object.
    */
-  values<T>(o: T): CheckNonNullable<T, unknown[]>;
+  values<T>(o: CheckNonNullable<T>): unknown[];
 
   /**
    * Returns an array of key/values of the enumerable properties of an object
@@ -29,16 +29,15 @@ interface ObjectConstructor {
    * Returns an array of key/values of the enumerable properties of an object
    * @param o Object that contains the properties and methods. This can be an object that you created or an existing Document Object Model (DOM) object.
    */
-  entries<T>(o: T): CheckNonNullable<T, [string, unknown][]>;
+  entries<T>(o: CheckNonNullable<T>): [string, unknown][];
 
   /**
    * Returns an object containing all own property descriptors of an object
    * @param o Object that contains the properties and methods. This can be an object that you created or an existing Document Object Model (DOM) object.
    */
-  getOwnPropertyDescriptors<T>(o: T): CheckNonNullable<
-    T,
-    { [P in keyof T]: TypedPropertyDescriptor<T[P]> } & {
-      [x: string]: PropertyDescriptor;
-    }
-  >;
+  getOwnPropertyDescriptors<T>(o: CheckNonNullable<T>): {
+    [P in keyof T]: TypedPropertyDescriptor<T[P]>;
+  } & {
+    [x: PropertyKey]: PropertyDescriptor;
+  };
 }
diff --git a/lib/lib.es5.d.ts b/lib/lib.es5.d.ts
index 0d9d716..2528d74 100644
--- a/lib/lib.es5.d.ts
+++ b/lib/lib.es5.d.ts
@@ -1,12 +1,19 @@
-type First<T> = T extends [any] ? T[0] : unknown;
+type Cast<T, U> = T extends U ? T : U;
 
-type UnionToIntersection<T> = (
-  T extends any ? (arg: T) => void : never
-) extends (arg: infer F) => void
-  ? F
-  : unknown;
+/**
+ * Make all properties in T writable
+ */
+type Writable<T> = {
+  -readonly [P in keyof T]: T[P];
+};
 
-type CheckNonNullable<T, U> = [T] extends [NonNullable<T>] ? U : never;
+type Intersect<T extends readonly any[]> = ((
+  ...args: { [K in keyof T]: Cast<Writable<T[K]>, {}> }
+) => void) extends (...args: { [K in keyof T]: infer S }) => void
+  ? S
+  : never;
+
+type CheckNonNullable<T> = [T] extends [null | undefined] ? never : T;
 
 /**
  * Evaluates JavaScript code and executes it.
@@ -41,7 +48,7 @@ interface ObjectConstructor {
    * Returns the prototype of an object.
    * @param o The object that references the prototype.
    */
-  getPrototypeOf<T>(o: T): CheckNonNullable<T, unknown>;
+  getPrototypeOf<T>(o: CheckNonNullable<T>): unknown;
 
   /**
    * Gets the own property descriptor of the specified object.
@@ -50,16 +57,16 @@ interface ObjectConstructor {
    * @param p Name of the property.
    */
   getOwnPropertyDescriptor<T>(
-    o: T,
+    o: CheckNonNullable<T>,
     p: PropertyKey
-  ): CheckNonNullable<T, PropertyDescriptor | undefined>;
+  ): PropertyDescriptor | undefined;
 
   /**
    * Returns the names of the own properties of an object. The own properties of an object are those that are defined directly
    * on that object, and are not inherited from the object's prototype. The properties of an object include both fields (objects) and functions.
    * @param o Object that contains the own properties.
    */
-  getOwnPropertyNames<T>(o: T): CheckNonNullable<T, string[]>;
+  getOwnPropertyNames<T>(o: CheckNonNullable<T>): string[];
 
   /**
    * Creates an object that has the specified prototype or that has null prototype.
@@ -155,6 +162,13 @@ interface ObjectConstructor {
 }
 
 interface CallableFunction extends Function {
+  /**
+   * For a given function, creates a bound function that has the same body as the original function.
+   * The this object of the bound function is associated with the specified object, and has the specified initial parameters.
+   * @param thisArg The object to be used as the this object.
+   */
+  bind<T>(this: T, thisArg: ThisParameterType<T>): OmitThisParameter<T>;
+
   /**
    * For a given function, creates a bound function that has the same body as the original function.
    * The this object of the bound function is associated with the specified object, and has the specified initial parameters.
@@ -169,6 +183,13 @@ interface CallableFunction extends Function {
 }
 
 interface NewableFunction extends Function {
+  /**
+   * For a given function, creates a bound function that has the same body as the original function.
+   * The this object of the bound function is associated with the specified object, and has the specified initial parameters.
+   * @param thisArg The object to be used as the this object.
+   */
+  bind<T>(this: T, thisArg: any): T;
+
   /**
    * For a given function, creates a bound function that has the same body as the original function.
    * The this object of the bound function is associated with the specified object, and has the specified initial parameters.
diff --git a/tests/src/es2015.core.ts b/tests/src/es2015.core.ts
index bec0f1a..ddf9bbb 100644
--- a/tests/src/es2015.core.ts
+++ b/tests/src/es2015.core.ts
@@ -36,7 +36,7 @@ import { expectError, expectType } from "tsd";
 
 // ObjectConstructor
 {
-  expectType<never>(Object.assign(null));
+  expectError(Object.assign(null));
   const obj1 = Object.assign({ foo: 123 });
   expectType<{ foo: number }>(obj1);
   const obj2 = Object.assign({ foo: 123 }, { bar: "wow" });
@@ -48,6 +48,8 @@ import { expectError, expectType } from "tsd";
     { baz: true }
   );
   expectType<({ foo: number } | { bar: string }) & { baz: boolean }>(obj4);
+  expectType<symbol[]>(Object.getOwnPropertySymbols([]));
+  expectError(Object.getOwnPropertySymbols(null));
   const obj5 = Object.setPrototypeOf({ foo: 123 }, { bar: "wow" });
   expectType<{ foo: number } & { bar: string }>(obj5);
 }
diff --git a/tests/src/es2017.object.ts b/tests/src/es2017.object.ts
index 904f8bb..588ca29 100644
--- a/tests/src/es2017.object.ts
+++ b/tests/src/es2017.object.ts
@@ -1,4 +1,4 @@
-import { expectType } from "tsd";
+import { expectError, expectType } from "tsd";
 
 function createGenericRecord<K extends string, V>(
   keys: K[],
@@ -8,9 +8,9 @@ function createGenericRecord<K extends string, V>(
 }
 
 {
-  expectType<never>(Object.values(null));
-  expectType<never>(Object.entries(null));
-  expectType<never>(Object.getOwnPropertyDescriptors(null));
+  expectError(Object.values(null));
+  expectError(Object.entries(null));
+  expectError(Object.getOwnPropertyDescriptors(null));
 
   const obj1: { [k: string]: number } = { foo: 123 };
   const values1 = Object.values(obj1);
@@ -42,11 +42,11 @@ function createGenericRecord<K extends string, V>(
   expectType<(number | { [k: string]: number })[]>(values5);
   expectType<[string, number | { [k: string]: number }][]>(entries5);
 }
-function test<T>(obj: T) {
+function test<T>(obj: CheckNonNullable<T>) {
   const values = Object.values(obj);
   expectType<unknown>(values[0]);
 
   const entries = Object.entries(obj);
   expectType<string>(entries[0][0]);
-  const v: unknown = entries[0][1];
+  expectType<unknown>(entries[0][1]);
 }
diff --git a/tests/src/es5.ts b/tests/src/es5.ts
index 972bfa5..1ac2da7 100644
--- a/tests/src/es5.ts
+++ b/tests/src/es5.ts
@@ -8,15 +8,15 @@ expectType<{ foo: number }>(Object({ foo: 123 }));
 expectType<{}>(Object(123));
 // Object.getPrototypeOf
 expectType<unknown>(Object.getPrototypeOf([]));
-expectType<never>(Object.getPrototypeOf(null));
+expectError(Object.getPrototypeOf(null));
 // Object.getOwnPropertyDescriptor
 expectType<PropertyDescriptor | undefined>(
   Object.getOwnPropertyDescriptor([], "foo")
 );
-expectType<never>(Object.getOwnPropertyDescriptor(null, "foo"));
+expectError(Object.getOwnPropertyDescriptor(null, "foo"));
 // Object.getOwnPropertyNames
 expectType<string[]>(Object.getOwnPropertyNames([]));
-expectType<never>(Object.getOwnPropertyNames(null));
+expectError(Object.getOwnPropertyNames(null));
 // Object.create
 expectType<{}>(Object.create(null));
 expectType<{ foo: number }>(Object.create({ foo: 123 }));
@@ -123,7 +123,7 @@ expectType<{ foo: number; bar: string; baz: boolean }>(
   class Foo {
     constructor(private a: number, private b: number) {}
   }
-  expectType<new (a: number, b: number) => Foo>(Foo.bind(null));
+  expectType<typeof Foo>(Foo.bind(null));
   expectType<new (b: number) => Foo>(Foo.bind(null, 123));
   expectType<new () => Foo>(Foo.bind(null, 123, 456));
   expectError(Foo.bind(null, 123, 456, 789));