diff --git a/chatlearn/chatlearn.py b/chatlearn/chatlearn.py
index fa19f5c3..369842ed 100644
--- a/chatlearn/chatlearn.py
+++ b/chatlearn/chatlearn.py
@@ -101,7 +101,7 @@ def _run_algorithm(self, algo_args) -> None:
                 for arg in algo_args.hydra_args:
                     if '=' in arg:
                         key, value = arg.split('=', 1)
-                        if OmegaConf.select(external_cfg, key):
+                        if OmegaConf.select(external_cfg, key) is not None:
                             OmegaConf.update(external_cfg, key, value)
                 cfg = OmegaConf.merge(cfg, external_cfg)
             cfg = OmegaConf.to_object(cfg)