title: NUnit Raise event on abstract class attempt fails
body: <p>Why does this NUnit test below fail? Or why is the event is never triggered?</p>
  
  <pre><code>public interface IGo
  {
      event Action&lt;bool&gt; GoNow;
  }
  
  public abstract class Goer : IGo
  {
      public virtual event Action&lt;bool&gt; GoNow = delegate {};
  }
  
  [Test]
  public void VerifyNUnitRaise()
  {
      var mock = new Mock&lt;Goer&gt; {CallBase = true};
      var hit = false;
      mock.Object.GoNow += b =&gt; hit = b;
      mock.Raise(g =&gt; g.GoNow += null, true);
  
      Assert.IsTrue(hit);
  }
  </code></pre>