Add explicit return to make mypy happy

Cito · Cito · commit ef97e3d5d0e7 · 2019-07-18T19:34:06.000+02:00
diff --git a/graphql/utils/get_field_def.py b/graphql/utils/get_field_def.py
@@ -36,3 +36,5 @@ def get_field_def(
 
     elif isinstance(parent_type, (GraphQLObjectType, GraphQLInterfaceType)):
         return parent_type.fields.get(name)
+
+    return None
