This code has a very subtle bug:
What is the problem with this code? It is an obvious try at bridging an annoying design issue in C#, the fact that invoking an event with no subscribers throws a null reference exception. It should have been a no op, but that is another issue.
The copying to a separate variable is also common, because this allow you to avoid subtle mutli threading bug. The problem is this code it that it contains a bug.
The nullability check should have been made on the handler local variable, like this:
As the code stands, it has a very subtle bug, that will only appear in multi threaded scenarios, and even then, not always. The fixed code handle the issue correctly. But on first glance, they both seem to be doing the same thing.