code: @Override
  	public MemcachedNode getPrimary( final String key ) {
          final String nodeId = getNodeId( key );
          final MemcachedNode result = _nodesMap.get( nodeId );
          if ( result == null ) {
              throw new IllegalArgumentException( "No node found for key " + key + " (nodeId: " + nodeId + ", known nodeIds: " + _nodesMap.keySet() + ")" );
          }
          return result;
      }
docs: {@inheritDoc}