docs: void fireMemberStateChanged(AsteriskQueueMemberImpl member)
      {
          synchronized (listeners)
          {
              for (AsteriskQueueListener listener : listeners)
              {
                  try
                  {
                      listener.onMemberStateChange(member);
                  }
                  catch (Exception e)
                  {
                      logger.warn("Exception in onMemberStateChange()", e);
                  }
              }
          }
      }