 class="returnLabel">Returns:</span></dt>
<dd>The results of the send operation grouped by user. If it contains an empty set, then there was no open
 web socket session associated with given socket channel and user. The returned futures will return
 <code>null</code> on <a href="https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/Future.html?is-external=true#get--" title="class or interface in java.util.concurrent"><code>Future.get()</code></a> if the message was successfully delivered and otherw