Adds null checks to UriHelper and fixes typo

Author: jkotalik

src/Microsoft.AspNetCore.Http.Extensions/UriHelper.cs

@@ -53,6 +53,11 @@ public static string BuildAbsolute(
             QueryString query = new QueryString(),
             FragmentString fragment = new FragmentString())
         {
+            if (scheme == null)
+            {
+                throw new ArgumentNullException(nameof(scheme));
+            }
+
             var combinedPath = (pathBase.HasValue || path.HasValue) ? (pathBase + path).ToString() : "/";
 
             var encodedHost = host.ToString();
@@ -74,7 +79,7 @@ public static string BuildAbsolute(
         }
 
         /// <summary>
-        /// Seperates the given absolute URI string into components. Assumes no PathBase.
+        /// Separates the given absolute URI string into components. Assumes no PathBase.
         /// </summary>
         /// <param name="uri">A string representation of the uri.</param>
         /// <param name="scheme">http, https, etc.</param>
@@ -94,7 +99,7 @@ public static void FromAbsolute(
             {
                 throw new ArgumentNullException(nameof(uri));
             }
-            // Satisfy the out parameters
+
             path = new PathString();
             query = new QueryString();
             fragment = new FragmentString();
@@ -142,6 +147,11 @@ public static void FromAbsolute(
         /// <returns></returns>
         public static string Encode(Uri uri)
         {
+            if (uri == null)
+            {
+                throw new ArgumentNullException(nameof(uri));
+            }
+
             if (uri.IsAbsoluteUri)
             {
                 return BuildAbsolute(

test/Microsoft.AspNetCore.Http.Extensions.Tests/UriHelperTests.cs

@@ -1,6 +1,7 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
 using Xunit;
 
 namespace Microsoft.AspNetCore.Http.Extensions
@@ -128,5 +129,28 @@ public void FromAbsoluteToBuildAbsolute()
             Assert.Equal(query, resQuery);
             Assert.Equal(fragment, resFragment);
         }
+
+        [Fact]
+        public void BuildAbsoluteNullInputThrowsArgumentNullException()
+        {
+            var resHost = new HostString();
+            var resPath = new PathString();
+            var resQuery = new QueryString();
+            var resFragment = new FragmentString();
+            Assert.Throws<ArgumentNullException>(() => UriHelper.BuildAbsolute(null, resHost,  resPath, resPath,  resQuery,  resFragment));
+
+        }
+
+        [Fact]
+        public void FromAbsoluteNullInputThrowsArgumentNullException()
+        {
+            string resScheme = null;
+            var resHost = new HostString();
+            var resPath = new PathString();
+            var resQuery = new QueryString();
+            var resFragment = new FragmentString();
+            Assert.Throws<ArgumentNullException>(() => UriHelper.FromAbsolute(null, out resScheme, out resHost, out resPath, out resQuery, out resFragment));
+
+        }
     }
 }