title: Use of null check in event handler
body: <p>When checking if an event handler is null, is this done on a per-thread basis?</p>
  
  <p>Ensuring someone is listening to the event is done like this:</p>
  
  <pre><code>EventSeven += new DivBySevenHandler(dbsl.ShowOnScreen);
  </code></pre>
  
  <p>If I add code following this pattern above where I check for null, then why would I need a null check (<a href="http://www.codeproject.com/KB/cs/csevents01.aspx" rel="noreferrer">code taken from this site</a>). What am I missing?</p>
  
  <p>Also, what's the rule with events and GC?</p>