GitLab

* change to support optional outputs

* clang format

* add onnx test for better code coverage

* add corresponding onnx file

* fix review comments of handling optional program outputs

* clang format

* change onnx unit test to pass

* clang format

* refine onnx unit tests

* clang format

* remove unnecessary code

fix comments about enum rnn_direction, rnn_last_output, and added more tests to achieve better code coverage

fix comments. improve the implementation of parsing the ConstantFill operator, and add more tests for better code coverage.