@Override
    public Object initValue(Object struct) throws HiveException {
      Object initValue = this.baseWriter.initValue(null);
      this.settableObjInspector.setStructFieldData(struct, fieldRef, initValue);
      return struct;
    }
VectorExpressionWriterSetter helper for vector expression writers that use
settable ObjectInspector fields to assign the values.
This is used by the OrcStruct serialization (eg. CREATE TABLE ... AS ...)
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/VectorExpressionWriterFactory.java