void setNull(TimestampColumnVector outputColVector, int i) {
    outputColVector.setNullValue(i);
    outputColVector.isNull[i] = true;
    outputColVector.noNulls = false;
  }
Casts a string vector to a Timestamp vector.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/CastStringToTimestamp.java