@Override
  protected int getLength(ObjectInspector objectInspector, ByteArrayRef cachedByteArrayRef,
      int start, int fieldLen) {
    if (fieldLen == lengthNullSequence) {
      byte[] data = cachedByteArrayRef.getData();
      if (LazyUtils.compare(data, start, fieldLen,
          nullSequence.getBytes(), 0, lengthNullSequence) == 0) {
        return -1;
      }
    }
    return fieldLen;
  }
Construct a ColumnarStruct object with the TypeInfo. It creates the first
level object at the first place

@param oi
         the ObjectInspector representing the type of this LazyStruct.
@param notSkippedColumnIDs
         the column ids that should not be skipped
serde/src/java/org/apache/hadoop/hive/serde2/columnar/ColumnarStruct.java