In Blazor Nullable<TimeSpan> generates error "The value '' is not valid for 'Property'." when value is empty

[neoGeneva]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

Looks like this is related to the pull request #60498 "Limit types that get converted to null for empty/null input in NullableConverter", looks like TimeSpan should be included in the list.

I ran a script against all the NullableConverter types in WellKnownConverters.cs and it looks like there are several types defined there that won't deserialize to null.

• Int128
• UInt128
• Half
• TimeSpan
• Guid

var types = new[]
{
    typeof(char),
    typeof(bool),
    typeof(byte),
    typeof(sbyte),
    typeof(ushort),
    typeof(uint),
    typeof(ulong),
    typeof(Int128),
    typeof(short),
    typeof(int),
    typeof(long),
    typeof(UInt128),
    typeof(Half),
    typeof(float),
    typeof(double),
    typeof(decimal),
    typeof(DateOnly),
    typeof(DateTime),
    typeof(DateTimeOffset),
    typeof(TimeSpan),
    typeof(TimeOnly),
    typeof(Guid),
};

foreach (var type in types)
{
    var isSupportedUnderlyingType = IsSupportedUnderlyingType(type);

    if (!isSupportedUnderlyingType)
        Console.WriteLine(type.Name);
}

static bool IsSupportedUnderlyingType(Type type)
{
    return Type.GetTypeCode(type) != TypeCode.Object || IsSupportedUnderlyingObjectType(type);
}

static bool IsSupportedUnderlyingObjectType(Type type)
{
    return type == typeof(DateOnly) || type == typeof(TimeOnly) || type == typeof(DateTimeOffset);
}

Expected Behavior

A form value of "" should deserialize to null.

Steps To Reproduce

1. Create a Blazor server side app
2. Create a model object with a property of type Nullable?
3. Create a form that has that property in it
4. Submit the form with the value blank

Exceptions (if any)

No response

.NET Version

10.0.203

Anything else?

No response

[github-actions]

Triage Summary

Area: area-blazor — The issue is in WellKnownConverters.cs under src/Components/Endpoints/src/FormMapping/, directly related to Blazor's form mapping NullableConverter.
Type: bug — Empty form field values for Nullable<TimeSpan>, Nullable<Guid>, Nullable<Int128>, Nullable<UInt128>, and Nullable<Half> fail to deserialize to null, producing a validation error. The reporter also identifies the root cause: IsSupportedUnderlyingObjectType in the NullableConverter logic is missing these types (only DateOnly, TimeOnly, and DateTimeOffset are listed), which is likely an incomplete fix from PR #60498.

Regression Info

• Previously working version: Not explicitly stated
• Broken since: The reporter links this to PR Limit types that get converted to null for empty/null input in NullableConverter #60498 ("Limit types that get converted to null for empty/null input in NullableConverter"), suggesting it was introduced or exacerbated by that change. The types Int128, UInt128, Half, TimeSpan, and Guid were not included in the IsSupportedUnderlyingObjectType allowlist.

Potential Duplicates

• None found

Notes

The fix should be to add TimeSpan, Guid, Int128, UInt128, and Half to the IsSupportedUnderlyingObjectType check in the NullableConverter (or equivalent logic in WellKnownConverters.cs). The reporter has already done the legwork to identify all affected types.

Generated by Issue Triage Agent for dotnet/aspnetcore for issue #66607 · ● 251.7K · ◷