fix: address review comments (iteration #1)

Author: aviruthen

sagemaker-train/src/sagemaker/train/tuner.py

@@ -1504,10 +1504,10 @@ def _build_training_job_definition(self, inputs):
                     model_trainer.stopping_condition.max_wait_time_in_seconds
                 )
 
-        # Get environment variables from model_trainer
-        env = getattr(model_trainer, "environment", None)
-        if not env or not isinstance(env, dict):
-            env = None
+        # Get environment variables from model_trainer.
+        # environment is a defined attribute on ModelTrainer (dict | None).
+        # We pass it through as-is; even an empty dict is valid for the API.
+        env = model_trainer.environment
 
         definition = HyperParameterTrainingJobDefinition(
             algorithm_specification=algorithm_spec,

sagemaker-train/tests/unit/train/test_tuner.py

@@ -639,7 +639,11 @@ def test_build_training_job_definition_with_none_environment(self):
         assert definition.environment is None, "Environment should be None when not set"
 
     def test_build_training_job_definition_with_empty_environment(self):
-        """Test that _build_training_job_definition handles empty environment gracefully."""
+        """Test that _build_training_job_definition passes through empty environment.
+
+        An empty dict is valid for the SageMaker API, so we pass it through as-is
+        rather than silently converting it to None.
+        """
         mock_trainer = _create_mock_model_trainer()
         mock_trainer.environment = {}
 
@@ -651,6 +655,6 @@ def test_build_training_job_definition_with_empty_environment(self):
 
         definition = tuner._build_training_job_definition(None)
 
-        assert definition.environment is None, (
-            "Environment should be None when empty dict is provided"
+        assert definition.environment == {}, (
+            "Empty dict environment should be passed through as-is"
         )