diff --git a/tests/metagpt/actions/test_action_node.py b/tests/metagpt/actions/test_action_node.py
index 338d87242..58a6dd517 100644
--- a/tests/metagpt/actions/test_action_node.py
+++ b/tests/metagpt/actions/test_action_node.py
@@ -306,6 +306,7 @@ def test_optional():
     mapping = {
         "Logic Analysis": (Optional[List[Tuple[str, str]]], Field(default=None)),
         "Task list": (Optional[List[str]], None),
+        "Plan": (Optional[str], ""),
         "Anything UNCLEAR": (Optional[str], None),
     }
     m = {"Anything UNCLEAR": "a"}