Added check of RequiresValidationContext before calling IsValid (#110647

)

* Added check of RequiresValidationContext before calling IsValid

The fix is done to avoid NRE when CompareAttribute's implementation of IsValid(object? value, ValidationContext validationContext) is called with validationContext == null.

Fix #42490

* Throw exception if validation context is null

* Unit test

src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/CompareAttribute.cs

@@ -33,6 +33,8 @@ public override string FormatErrorMessage(string name) =>
             Justification = "The ctor is marked with RequiresUnreferencedCode informing the caller to preserve the other property.")]
         protected override ValidationResult? IsValid(object? value, ValidationContext validationContext)
         {
+            ArgumentNullException.ThrowIfNull(validationContext);
+
             var otherPropertyInfo = validationContext.ObjectType.GetRuntimeProperty(OtherProperty);
             if (otherPropertyInfo == null)
             {

src/libraries/System.ComponentModel.Annotations/tests/System/ComponentModel/DataAnnotations/CompareAttributeTests.cs

@@ -99,6 +99,15 @@ public static void Validate_PropertyHasDisplayName_UpdatesFormatErrorMessageToCo
             Assert.Contains("CustomDisplayName", newErrorMessage);
         }
 
+        [Fact]
+        public static void IsValid_ValidationContextNull_ThrowsArgumentNullException()
+        {
+            var attribute = new CompareAttribute(nameof(CompareObject.ComparePropertyWithDisplayName));
+            var compareObject = new CompareObject("test");
+
+            Assert.Throws<ArgumentNullException>(() => attribute.IsValid(compareObject.CompareProperty));
+        }
+
         private class DerivedCompareAttribute : CompareAttribute
         {
             public DerivedCompareAttribute(string otherProperty) : base(otherProperty) { }