Fix optional non-nullable struct query parameters with = default throwing in RequestDelegateFactory

[Copilot]

Reflection reports DefaultValue == null for non-nullable struct parameters with = default (e.g., Guid, DateTime, TimeSpan). CreateDefaultValueExpression was passing that null directly to Expression.Constant(null, parameterType), which throws ArgumentException: Argument types do not match for non-nullable value types.

Description

• RequestDelegateFactory.cs: In CreateDefaultValueExpression, when defaultValue is null and parameterType is a non-nullable value type, use Expression.Default(parameterType) instead of Expression.Constant(null, parameterType).
• RequestDelegateCreationTests.QueryParameters.cs: Added tests covering Guid and DateTime optional parameters with = default, both with and without a query string value provided. Tests are placed in RequestDelegateCreationTests.QueryParameters.cs so they run against both RequestDelegateFactory (via RuntimeCreationTests) and RequestDelegateGenerator (via CompileTimeCreationTests).

// Previously threw ArgumentException at first request; now works correctly
app.MapGet("/ok", ([FromQuery] Guid id = default, [FromQuery] DateTime date = default) => Results.Ok());

• You've read the Contributor Guide and Code of Conduct.
• You've included unit or integration tests for your change, where applicable.
• You've included inline docs for your change, where applicable.
• There's an open issue for the PR that you are making. If you'd like to propose a new feature or change, please open an issue to discuss the change or find an existing issue.

[Copilot]

Pull request overview

Fixes a runtime exception in minimal API binding when optional non-nullable struct query parameters use = default (reflection reports DefaultValue == null, which previously caused an invalid Expression.Constant(null, valueType)).

Changes:

• Update RequestDelegateFactory.CreateDefaultValueExpression to use Expression.Default(parameterType) when defaultValue is null for non-nullable value types.
• Add generator/runtime coverage for optional [FromQuery] Guid and [FromQuery] DateTime parameters declared with = default, with and without query values.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/Http/Http.Extensions/src/RequestDelegateFactory.cs	Prevents ArgumentException by emitting a default(T) expression for non-nullable value types when reflection returns DefaultValue == null.
src/Http/Http.Extensions/test/RequestDelegateGenerator/RequestDelegateCreationTests.QueryParameters.cs	Adds regression tests for optional struct query parameters using = default across runtime (factory) and compile-time (generator) paths.

[Copilot]

queryValue is passed as null via [InlineData(null, ...)], but the parameter is declared as non-nullable string. Consider changing it to string? queryValue so the signature matches the test data and avoids nullable-analysis warnings.

[Copilot]

queryValue is provided as null in one [InlineData] case, but the parameter is declared string (non-nullable). Update it to string? queryValue to accurately model the test inputs and avoid nullable warnings.

Suggested change

	public async Task CanSetDateTimeParamAsOptionalWithDefaultValue(string queryValue, string expectedResponse)
	public async Task CanSetDateTimeParamAsOptionalWithDefaultValue(string? queryValue, string expectedResponse)