Null pointer exception on .iterator() call
<p>I'm getting a strange NullPointerException, evidently thrown by the following line of code:</p>

<pre><code>Iterator&lt;Note&gt; it = notes.iterator();
</code></pre>

<p>I've checked, and at the time the java.util.TreeSet <code>notes</code> is always non-null (with 15 elements). The TreeSet API says nothing about <code>iterator()</code> throwing NullPointerExceptions. What else could be going here?</p>
