Fix --results-dir (#5269)

com.unity.ml-agents/CHANGELOG.md

 - Removed additional memory allocations that were occurring due to assert messages and iterating of DemonstrationRecorders. (#5246)
 - Fixed a bug where agent trying to access unintialized fields when creating a new RayPerceptionSensorComponent on an agent. (#5261)
 
+#### ml-agents / ml-agents-envs / gym-unity (Python)
+- Fixed a bug where --results-dir has no effect. (#5269)
+
 ## [1.9.1-preview] - 2021-04-13
 ### Major Changes
 #### ml-agents / ml-agents-envs / gym-unity (Python)

ml-agents/mlagents/trainers/cli_utils.py

         help="(Removed) Use the TensorFlow framework.",
     )
     argparser.add_argument(
-        "--results-dir", default="results", help="Results base directory"
+        "--results-dir",
+        default="results",
+        action=DetectDefault,
+        help="Results base directory",
     )
 
     eng_conf = argparser.add_argument_group(title="Engine Configuration")

ml-agents/mlagents/trainers/tests/test_learn.py

         "--num-envs=2",
         "--no-graphics",
         "--debug",
+        "--results-dir=myresults",
     ]
 
     opt = parse_command_line(full_args)
     assert opt.debug is True
     assert opt.checkpoint_settings.inference is True
     assert opt.checkpoint_settings.resume is True
+    assert opt.checkpoint_settings.results_dir == "myresults"
 
 
 @patch("builtins.open", new_callable=mock_open, read_data=MOCK_YAML)