Fix python client attribute output to handle None (#265)

In testing 3.3.0 with the Python SDK, turns out routes without the attribute defined have values of "None". This PR tweaks the logic from #262 to handle None, and adds a regression test.

Also updates the version to so as a follow I can publish the fix.

setup.py

@@ -39,7 +39,7 @@
 
 dist = setup(
     name='stone',
-    version='3.3.0',
+    version='3.3.1',
     install_requires=install_reqs,
     setup_requires=setup_requires,
     tests_require=test_reqs,

stone/backends/python_client.py

@@ -396,7 +396,7 @@ def _generate_docstring_for_func(self, namespace, arg_data_type,
         attrs_lines = []
         if self.args.attribute_comment and attrs:
             for attribute in self.args.attribute_comment:
-                if attribute in attrs:
+                if attribute in attrs and attrs[attribute] is not None:
                     attrs_lines.append('{}: {}'.format(attribute, attrs[attribute]))
 
         if not fields and not overview and not attrs_lines:

test/test_python_client.py

@@ -253,6 +253,37 @@ def files_get_metadata(self):
         ''')
         self.assertEqual(result, expected)
 
+    def test_route_with_none_attribute_in_docstring(self):
+        # type: () -> None
+
+        route = ApiRoute('get_metadata', 1, None)
+        route.set_attributes(None, None, Void(), Void(), Void(), {
+            'scope': 'events.read', 'another_attribute': None
+        })
+        ns = ApiNamespace('files')
+        ns.add_route(route)
+
+        result = self._evaluate_namespace(ns)
+        expected = textwrap.dedent('''\
+            def files_get_metadata(self):
+                """
+                Route attributes:
+                    scope: events.read
+
+                :rtype: None
+                """
+                arg = None
+                r = self.request(
+                    files.get_metadata,
+                    'files',
+                    arg,
+                    None,
+                )
+                return None
+
+        ''')
+        self.assertEqual(result, expected)
+
     def test_route_with_attributes_and_doc_in_docstring(self):
         # type: () -> None
         """