title: Socket.io null in room
body: <p>Is it possible to have <code>null</code> in a socket.io room?</p>
  
  <p>I mean when I am listing my rooms (<code>io.sockets.manager.rooms</code>) I get this:</p>
  
  <pre><code> ["":[ ... ], "/dwQmEetnGTuHlLwwGe71rDG5":[null]...]
  </code></pre>
  
  <p>It seems strange to me to get <code>[null]</code> in a room, which supposed to hold the <code>socketID</code> for that room.</p>