Fix null value in ResultPath

Fixes #45

Author: tuliocasagrande

src/stepfunctions/steps/states.py

@@ -68,7 +68,7 @@ def to_dict(self):
         result = {}
         # Common fields
         for k, v in self.fields.items():
-            if v is not None:
+            if v is not None or k == 'result_path':
                 k = to_pascalcase(k)
                 if k == to_pascalcase(Field.Parameters.value):
                     result[k] = self._replace_placeholders(v)

tests/unit/test_steps.py

@@ -346,4 +346,24 @@ def test_retry_fail_for_unsupported_state():
     c1 = Choice('My Choice')
 
     with pytest.raises(ValueError):
-        c1.add_catch(Catch(error_equals=["States.NoChoiceMatched"], next_step=Fail("ChoiceFailed")))
+        c1.add_catch(Catch(error_equals=["States.NoChoiceMatched"], next_step=Fail("ChoiceFailed")))
+
+
+def test_result_path_none():
+    task_state = Task('Task', resource='arn:aws:lambda:us-east-1:1234567890:function:StartLambda', result_path=None)
+    assert task_state.to_dict() == {
+        'Type': 'Task',
+        'Resource': 'arn:aws:lambda:us-east-1:1234567890:function:StartLambda',
+        'ResultPath': None,
+        'End': True
+    }
+
+
+def test_result_path_none_converted_to_null():
+    task_state = Task('Task', resource='arn:aws:lambda:us-east-1:1234567890:function:StartLambda', result_path=None)
+    assert '"ResultPath": null' in task_state.to_json()
+
+
+def test_default_result_path_not_converted_to_null():
+    task_state = Task('Task', resource='arn:aws:lambda:us-east-1:1234567890:function:StartLambda')
+    assert '"ResultPath": null' not in task_state.to_json()