code: public <T extends Memory> T getNodeMemory(MemoryFactory<T> node) {
          return nodeMemories.getNodeMemory( node, this );
      }
docs: Retrieve the <code>JoinMemory</code> for a particular
  <code>JoinNode</code>.
  @param node
  The <code>JoinNode</code> key.
  @return The node's memory.