public static void setNullColIsNullValue(ColumnVector cv, int rowIndex) {
    cv.isNull[rowIndex] = true;
    if (cv.noNulls) {
      cv.noNulls = false;
    }
  }
Sets the IsNull value for ColumnVector at specified index
@param cv
@param rowIndex
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/VectorizedBatchUtil.java