code: public String getMemcachedNodeId() {
          final String nodeId = _nodeIds.get( _random.nextInt( _nodeIds.size() ) );
          return isNodeAvailable( nodeId ) ? nodeId : getAvailableNodeId( nodeId );
      }
docs: Get the next random, available node id. If no node is available, <code>null</code>
  is returned.
  @return a nodeId or <code>null</code>.