@Override
  public void setNextNonNullKey(int nonNullKeyPosition) {
    super.setNextNonNullKey(nonNullKeyPosition);

    currentHasAnyNulls = hasAnyNulls[nonNullKeyPosition];
  }
A key series of a multiple columns of keys where the keys get serialized.
(Or, it can be 1 column).
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/keyseries/VectorKeySeriesMultiSerialized.java