EnsureValidDataType should reject whitespaces in DataTypeAttribute.Cu…

…stomDataType property because it is mandatory and it does not make sense that the property is whitespaces. (#14845)

Modify Ctor_String(string customDataType) test to validate whitespaces adding new InlineData.

Fix #4465

src/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/DataTypeAttribute.cs

@@ -115,7 +115,7 @@ public override bool IsValid(object value)
         /// <exception cref="InvalidOperationException"> is thrown if the current attribute is ill-formed.</exception>
         private void EnsureValidDataType()
         {
-            if (DataType == DataType.Custom && string.IsNullOrEmpty(CustomDataType))
+            if (DataType == DataType.Custom && string.IsNullOrWhiteSpace(CustomDataType))
             {
                 throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture,
                     SR.DataTypeAttribute_EmptyDataTypeString));

src/System.ComponentModel.Annotations/tests/DataTypeAttributeTests.cs

@@ -68,14 +68,15 @@ public static void GetDataTypeName_InvalidDataType_ThrowsIndexOutOfRangeExceptio
         [Theory]
         [InlineData("CustomValue")]
         [InlineData("")]
+        [InlineData(" ")]
         [InlineData(null)]
         public static void Ctor_String(string customDataType)
         {
             DataTypeAttribute attribute = new DataTypeAttribute(customDataType);
             Assert.Equal(DataType.Custom, attribute.DataType);
             Assert.Equal(customDataType, attribute.CustomDataType);
 
-            if (string.IsNullOrEmpty(customDataType))
+            if (string.IsNullOrWhiteSpace(customDataType))
             {
                 Assert.Throws<InvalidOperationException>(() => attribute.GetDataTypeName());
                 Assert.Throws<InvalidOperationException>(() => attribute.Validate(new object(), s_testValidationContext));