code: @Override
      public String getRack(final InetAddress endpoint)
      {
          final NodeData nodeData = nodeDataMap.get(endpoint);
          return nodeData != null ? nodeData.rack : defaultNodeData.rack;
      }
docs: Returns the name of the rack for the endpoint, or {@code UNKNOWN} if not known.
  
  @return the name of the data center for the endpoint, or {@code UNKNOWN} if not known