[GrahamTheCoder]

Fixes #1298

Summary

VB lets the parentheses be omitted when there are no parameters, leaving a null ParameterList.

• Delegate Sub Callback / Delegate Function Provider As Integer crashed with "Value cannot be null (parameterList)".
• A custom event's RaiseEvent accessor without parentheses silently lost its generated On<Event>() method.

Root cause: each call site handled the null parameter list on its own, and some did not handle it at all. Fix: a shared AcceptParameterListAsync extension (in SyntaxNodeVisitorExtensions) that returns an empty C# parameter list for null. It is now used at every VB parameter list conversion: delegates, methods, Declare, constructors, operators, lambdas and the property/RaiseEvent accessor paths. The existing ad-hoc ?? ParameterList() fallbacks were replaced by it.

Tests added

• Delegates: Delegate Sub Callback, Delegate Function Provider As Integer, and the generic form without parentheses.
• Custom event with a parameterless RaiseEvent accessor without parentheses: OnMyEvent() is now emitted and called.
• Parameterless Declare Sub/Declare Function, Sub New, Sub and Function without parentheses.

The delegate and RaiseEvent tests were confirmed red for the right reason before the fix.

For the reviewer

• The helper and the call-site changes are in one commit rather than a separate pure-refactor commit first.
• The blind subagent review round was not run. I had no way to spawn a subagent in this session.
• Coverage on the changed lines was not collected.

Full suite

1429 passed, 0 failed, 5 skipped. The master baseline file was empty, so there was nothing to compare against, but there were no failures.

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