diff --git a/dargs/dargs.py b/dargs/dargs.py
index 6a7c87c..e98c7a9 100644
--- a/dargs/dargs.py
+++ b/dargs/dargs.py
@@ -900,7 +900,7 @@ def gen_doc_flag(self, path: Optional[List[str]] = None, **kwargs) -> str:
             realdoc,
             targetdoc,
         ]
-        return "\n".join(filter(None.__ne__, allparts))
+        return "\n".join([x for x in allparts if x is not None])
 
     def _make_cpath(
         self, cname: str, path: Optional[List[str]] = None, showflag: bool = False