Fix RequestDelegateFactory to handle nullable types correctly in empty request body scenarios

[opuzakov]

Fix RequestDelegateFactory to handle nullable types correctly in empty request body scenarios

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Description

This change fixes an issue where RequestDelegateFactory would incorrectly handle nullable parameter types when the request body is empty (aligning behavior with the controller-based API)

The changes include:

• Add nullable type detection
• Additional test coverage for nullable parameter types with an empty request body

Fixes #57055

[dotnet-policy-service]

Thanks for your PR, @@opuzakov. Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[Copilot]

Pull Request Overview

This PR fixes an issue where RequestDelegateFactory incorrectly handled nullable parameter types when the request body is empty, ensuring behavior consistency with controller-based APIs.

• Adds nullable type detection to distinguish between regular value types and nullable value types
• Updates the default value assignment logic to leave nullable types as null when the request body is empty
• Includes comprehensive test coverage for the nullable parameter scenario

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
RequestDelegateFactory.cs	Adds nullable type detection and fixes default value assignment logic for empty request bodies
RequestDelegateFactoryTests.cs	Adds test case to verify nullable parameters are handled correctly with empty request bodies

[Copilot]

[nitpick] Consider extracting the complex condition into a well-named local variable or method to improve readability. For example: var shouldCreateDefaultValueType = allowEmptyRequestBody && bodyType.IsValueType && !isNullableType;

Suggested change

	if (allowEmptyRequestBody && bodyType.IsValueType && !isNullableType) // Nullable types should be left null
	var shouldCreateDefaultValueType = allowEmptyRequestBody && bodyType.IsValueType && !isNullableType;
	if (shouldCreateDefaultValueType) // Nullable types should be left null

[opuzakov]

@dotnet-policy-service agree