code: public void reset() {
      if (isConstant) return;
  
      if (childColumns != null) {
        for (ColumnVector c: childColumns) {
          ((WritableColumnVector) c).reset();
        }
      }
      elementsAppended = 0;
      if (numNulls > 0) {
        putNotNulls(0, capacity);
        numNulls = 0;
      }
    }
docs: Resets this column for writing. The currently stored values are no longer accessible.