[bigdevlarry]

ReferenceHandler::prepareArguments() now passes an explicit null through to a nullable parameter. Before, isset() treated it as a missing argument, addressing issue #640

Motivation and Context

prepareArguments() tested isset($arguments[$paramName]), so an argument the client sent as null looked missing. A parameter such as ?string $category = 'books' received 'books' instead of null. The schema allows null and the client sent it, but the handler ran with a different value. The check now also accepts a key that is present with a null value when the parameter allows null.

How Has This Been Tested?

I added a unit test, testHandlePassesAnExplicitNullToANullableParameterWithADefault. It checks that an explicit null gives NULL and that an omitted argument still gives the default 'books'.

Breaking Changes

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Additional context

[Copilot]

🟢 Approval recommended

No active review issues were identified for the change preserving explicit null arguments while retaining defaults for omitted parameters.

No open issues 🎉

What changed in this PR

Fixes issue #640 by preserving explicit null values for nullable tool parameters in ReferenceHandler, while retaining default values when arguments are omitted.

Changes:

• Distinguishes an explicitly supplied null from a missing argument for nullable parameters.
• Adds a regression test covering both explicit null and omitted arguments.
• Documents the fix in the changelog.

File	Description
tests/​Unit/​Capability/​Registry/​ReferenceHandlerTest.php	Tests explicit null handling and preservation of defaults for omitted arguments.
src/​Capability/​Registry/​ReferenceHandler.php	Accepts present argument keys with null values when the parameter allows null.
CHANGELOG.md	Records the nullable tool parameter fix.

_{Review effort: Balanced}