code: public K addNode(String node) {
          if (!Strings.isNullOrEmpty(node)) {
              nodes.add(node);
          }
          return (K) this;
      }
docs: Most cluster level APIs allow to specify which nodes to execute on (for example, getting the node stats for a node).
  Nodes can be identified in the APIs either using their internal node id, the node name, address, custom attributes,
  or just the _local node receiving the request. For example, here are some sample values for node:
  <p/>
  <pre>
  # Local   ->  _local
  
  # Address ->  10.0.0.3,10.0.0.4
  ->  10.0.0.*
  
  # Names   ->  node_name_goes_here
  ->  node_name_goes_*
  
  # Attributes (set something like node.rack: 2 in the config)
  ->  rack:2
  ->  ra*:2
  ->  ra*:2*
  </pre>