docs: public static TreeGraphNode getSubject(TreeGraphNode t) {
      TreeGraphNode subj = getNodeInRelation(t, NOMINAL_SUBJECT);
      if (subj != null) {
        return subj;
      }
      subj = getNodeInRelation(t, CLAUSAL_SUBJECT);
      if (subj != null) {
        return subj;
      } else {
        return getNodeInRelation(t, NOMINAL_PASSIVE_SUBJECT);
      }
    }