Clarify MA0093 only applies to event invocations, not regular method calls

[Copilot]

MA0093's scope was ambiguous—users expected it to flag all null EventArgs parameters, but it only triggers when raising events via delegate invocation.

Changes

• Updated rule title: "EventArgs should not be null when raising an event"
• Added explicit scope description to documentation
• Enhanced code example to demonstrate regular methods are not flagged:

class Test
{
    public event EventHandler MyEvent;

    void OnEvent()
    {
        MyEvent.Invoke(this, null);        // MA0093: flagged
        MyEvent.Invoke(this, EventArgs.Empty); // ok
        
        RegularMethod(null);               // not flagged by MA0093
    }

    void RegularMethod(EventArgs args) { }
}

The analyzer behavior is unchanged—only documentation was updated to clarify the rule applies exclusively to event delegate invocations (.Invoke() calls on events), not arbitrary methods accepting EventArgs.

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Original prompt

---

This section details on the original issue you should resolve

<issue_title>[F.Rq.] Equivalent of MA0093 but for arguments to regular method</issue_title>
<issue_description>Is your feature request related to a problem? Please describe.
MA0093 only flags when an event is 'raised' with (EventArgs?) null, not just any time a null literal of type EventArgs? appears. I now see the intent behind the rule but for a while I just assumed that it wasn't working in our codebase.

Describe the solution you'd like
Please clarify the rule's title and documentation.
Alternatively, check arguments to regular methods too, but I could always write my own Analyzer for that. Let me know if you'd be interested in having it in this project.

Describe alternatives you've considered
N/A

Additional context
N/A</issue_description>

<agent_instructions>Can you update the documentation to describe the current behavior?</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@meziantou The rule only reports when invoking a delegate with 2 parameters and the second is of type `EventArgs`. There are many other valid use-cases, so it would report many false-positive in existing codebases.

• Fixes [F.Rq.] Equivalent of MA0093 but for arguments to regular method #866

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