@Override
  public boolean isGroupResultNull() {
    return false;
  }
This class evaluates rank() for a PTF group.

Rank starts at 1; the same rank is streamed to the output column as repeated; after the last
group row, the rank is increased by the number of group rows.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/ptf/VectorPTFEvaluatorRank.java