fix dtype issues

Author: topper-123

pandas/core/dtypes/cast.py

@@ -1618,7 +1618,7 @@ def construct_1d_ndarray_preserving_na(
     array(['1.0', '2.0', None], dtype=object)
     """
 
-    if is_string_dtype(dtype):
+    if dtype is not None and dtype.kind == "U":
         subarr = lib.ensure_string_array(values, convert_na_value=False, copy=copy)
     else:
         subarr = np.array(values, dtype=dtype, copy=copy)

pandas/core/internals/construction.py

@@ -190,7 +190,7 @@ def init_ndarray(values, index, columns, dtype: Optional[DtypeObj], copy: bool):
     # the dtypes will be coerced to a single dtype
     values = _prep_ndarray(values, copy=copy)
 
-    if not is_dtype_equal(values.dtype, dtype):
+    if dtype is not None and not is_dtype_equal(values.dtype, dtype):
         try:
             values = construct_1d_ndarray_preserving_na(
                 values.ravel(), dtype=dtype, copy=False