private void assignStringNullsRepeating(int keyIndex, int index, int size, BytesColumnVector columnVector) {
    if (columnVector.isNull[0]) {
      for(int i = 0; i < size; ++i) {
        vectorHashKeyWrappers[i].assignNullString(keyIndex, index);
      }
    } else {
      for(int i = 0; i < size; ++i) {
        vectorHashKeyWrappers[i].assignString(
            index,
            columnVector.vector[0],
            columnVector.start[0],
            columnVector.length[0]);
      }
    }
  }
Helper method to assign values from a vector column into the key wrapper.
Optimized for double type, possible nulls, repeat values.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/wrapper/VectorHashKeyWrapperBatch.java