@Override
  public void addObjectField(String fieldName, Object member) {
    if (logger.isTraceEnabled()) {
      logger.trace("addObjectField fieldName: {}", fieldName);
    }
    if (fieldName == null) {
      throw new IllegalStateException("addObjectField:Object should have fieldname");
    }
    fieldList.add(new JSONFieldHolder(fieldName, member, FieldType.OBJECT));
  }
This class is intermediate class to create PdxInstance.
geode-core/src/main/java/org/apache/geode/pdx/internal/json/PdxInstanceSortedHelper.java