* optimize attr default value, test=develop

* refine, test=develop

* refine, test=develop

* refine, test=develop

* fix bug in AttrReader, test=develop

* fix bug, test=develop

* fix double_grad, test=develop

* refine, test=develop

* refine, test=develop

* fix checker null, test=develop

* for test, test=develop

* refine, test=develop

* refine, test=develop

* refine, test=develop

* refine, test=develop

* refine, test=develop

* refine, test=develop