title: Guava MultiMap and ConcurrentModificationException
body: <p>I don't understand why I get a ConcurrentModificationException when I iterate through this <code>multimap</code>.
  I read the following <a href="http://google-collections.googlecode.com/svn/trunk/javadoc/com/google/common/collect/Multimaps.html#synchronizedMultimap%28com.google.common.collect.Multimap%29" rel="noreferrer">entry</a>, but I am not sure if I understood the whole thing. 
  I tried to add a synchronized block. But my doubt is what to synchronize with, and when. </p>
  
  <p>The <code>multimap</code> is a field and created like this : </p>
  
  <pre><code>private Multimap&lt;GenericEvent, Command&gt; eventMultiMap =   
     Multimaps.synchronizedMultimap(HashMultimap.&lt;GenericEvent, Command&gt; create());
  </code></pre>
  
  <p>and used like this : </p>
  
  <pre><code>eventMultiMap.put(event, command);
  </code></pre>
  
  <p>and like this ( I tried to synchronize this part on the map, but without success )</p>
  
  <pre><code>for (Entry&lt;GenericEvent, Command&gt; entry : eventMultiMap.entries()) {
      if (entry.getValue().equals(command)) {
          eventMultiMap.remove(entry.getKey(), entry.getValue());
          nbRemoved++;
      }
  }
  </code></pre>