Refactor function name (#11210)

### What problem does this PR solve?

As title

### Type of change

- [x] Refactoring

---------

Signed-off-by: Jin Hai <haijin.chn@gmail.com>

rag/utils/s3_conn.py

@@ -164,7 +164,7 @@ class RAGFlowS3:
                 logging.exception(f"fail get {bucket}/{fnm}")
                 self.__open__()
                 time.sleep(1)
-        return
+        return None
 
     @use_prefix_path
     @use_default_bucket
@@ -193,7 +193,7 @@ class RAGFlowS3:
                 logging.exception(f"fail get url {bucket}/{fnm}")
                 self.__open__()
                 time.sleep(1)
-        return
+        return None
 
     @use_default_bucket
     def rm_bucket(self, bucket, *args, **kwargs):