@Override
  public Object readObject(String fieldName) {
    PdxField ft = blobType.getPdxField(fieldName);
    if (ft == null) {
      return null;
    }
    if (ft.getFieldType() != FieldType.OBJECT) {
      throw new PdxFieldTypeMismatchException(
          "Expected Object field but found field of type " + ft.getTypeIdString());
    }
    return readObject(ft);
  }
@return size of each variable length field offset
geode-core/src/main/java/org/apache/geode/pdx/internal/PdxReaderImpl.java