public void reset() {
    assert (refCount.get() == 0);
    if (!noNulls) {
      Arrays.fill(isNull, false);
    }
    noNulls = true;
    isRepeating = false;
    preFlattenNoNulls = true;
    preFlattenIsRepeating = false;
  }
Resets the column to default state
 - fills the isNull array with false
 - sets noNulls to true
 - sets isRepeating to false
storage-api/src/java/org/apache/hadoop/hive/ql/exec/vector/ColumnVector.java