Re-evaluate the nullabilty of eventName parameters in EventSourceActivity

[bartonjs]

The public methods on this internal type have xmldoc that says that eventName can be null.

runtime/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/EventSourceActivity.cs

Lines 167 to 180 in 363b7ad

	/// <summary>
	/// Writes an event associated with this activity.
	/// May only be called when the activity is in the Started state.
	/// </summary>
	/// <param name="eventName">
	/// The name to use for the event. If null, the name is determined from
	/// data's type.
	/// </param>
	/// <param name="data">The data to include in the event.</param>
	public void Write<T>(string? eventName, T data)
	{
	EventSourceOptions options = default;
	this.Write(this.eventSource, eventName, ref options, ref data);
	}

But one of the two ArgumentNullException sources in this class is for when eventName is null:

runtime/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/TraceLogging/EventSourceActivity.cs

Lines 260 to 268 in 363b7ad

	private void Write<T>(EventSource eventSource, string? eventName, ref EventSourceOptions options, ref T data)
	{
	if (this.state != State.Started)
	throw new InvalidOperationException(); // Write after stop.
	if (eventName == null)
	throw new ArgumentNullException();
	eventSource.Write(eventName, ref options, ref this.activityId, ref s_empty, ref data);
	}

maybe there's something I'm missing, though. Spotted in a code review for updating parameter names for ArgumentException types.

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[tarekgh]

@tommcdon @noahfalk I believe you own this one. could you please triage it?

[tommcdon]

@sywhang @josalem

[josalem]

If I recall, the nullability was added with dotnet/coreclr#24070 which looks like it may have been done in an automated fashion. Is the expectation that a nullable parameter can be null on invocation and not incur a ArgumentNullException? If so, then the parameter shouldn't be nullable. I can do an audit of EventSource*.cs later this week.

[bartonjs]

Is the expectation that a nullable parameter can be null on invocation and not incur a ArgumentNullException?

Yes, that's what it means to be marked as nullable. Nullability has no runtime impact, so declaring something to be not-null just means "this is going to throw an ArgumentNullException, or some less nice failure, if you pass null"

[noahfalk]

This was dead code and has been removed from the product entirely: #55575