code: private NodeInformationProvider getNodeInformationProvider(String node) {
          if (node == null) {
              return null;
          }
          return nodeInformationProviders.get(node);
      }
docs: Returns the NodeInformationProvider responsible for providing information
  (ie items) related to a given node or <tt>null</null> if none.<p>
  
  In MUC, a node could be 'http://jabber.org/protocol/muc#rooms' which means that the
  NodeInformationProvider will provide information about the rooms where the user has joined.
  
  @param node the node that contains items associated with an entity not addressable as a JID.
  @return the NodeInformationProvider responsible for providing information related
  to a given node.