code: public Set<TreeGraphNode> getDependents(TreeGraphNode t) {
      Set<TreeGraphNode> deps = Generics.newTreeSet();
      // todo [cdm]: Explore replacing this with direct iteration over Tree
      Set<Tree> nodes = root.subTrees();
      for (Iterator<Tree> it = nodes.iterator(); it.hasNext();) {
        TreeGraphNode node = (TreeGraphNode) it.next();
        TreeGraphNode gov = getGovernor(node);
        if (gov != null && gov == t) {
          deps.add(node);
        }
      }
      return deps;
    }
docs: Tries to return a <code>Set</code> of leaf (terminal) nodes
  which are the {@link GrammaticalRelation#DEPENDENT
  <code>DEPENDENT</code>}s of the given node <code>t</code>.
  Probably, <code>t</code> should be a leaf node as well.
  
  @param t a leaf node in this <code>GrammaticalStructure</code>
  @return a <code>Set</code> of nodes which are dependents of
  node <code>t</code>, or else <code>null</code>