improve style.

src/wikiq/__init__.py

@@ -49,14 +49,14 @@ class PersistMethod:
 
 async def diff_async(differ, last_text, text):
     try:
-        result =  await asyncio.wait_for(
+        return await asyncio.wait_for(
             asyncio.to_thread(differ.inline_json_diff, last_text, text),
             timeout=DIFF_TIMEOUT
         )
     except TimeoutError:
         print(f"WARNING! wikidiff2 timeout for rev: {row_buffer['revid'][i]}. Falling back to default limits.", file=sys.stderr)
-        return
-    return result
+        return None
+
 
 def calculate_persistence(tokens_added):
     return (sum([(len(x.revisions) - 1) for x in tokens_added]), len(tokens_added))