protected void setNull(LongColumnVector outputColVector, int i) {
    outputColVector.vector[i] = 1;
    outputColVector.isNull[i] = true;
    outputColVector.noNulls = false;
  }
Casts a string vector to a date vector.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/CastStringToDate.java