diff --git a/chatkit/actions.py b/chatkit/actions.py
index 689a8f1..9357c95 100644
--- a/chatkit/actions.py
+++ b/chatkit/actions.py
@@ -24,7 +24,7 @@ class ActionConfig(BaseModel):
 
 class Action(BaseModel, Generic[TType, TPayload]):
     type: TType = Field(default=TType, frozen=True)  # pyright: ignore
-    payload: TPayload
+    payload: TPayload | None = None
 
     @classmethod
     def create(
diff --git a/tests/helpers/mock_widget.py b/tests/helpers/mock_widget.py
index 2dde244..bd0dccd 100644
--- a/tests/helpers/mock_widget.py
+++ b/tests/helpers/mock_widget.py
@@ -615,6 +615,7 @@ async def handle_action(
         generate: Callable[[], AsyncIterator[ThreadStreamEvent]],
         save: Callable[[], AsyncIterator[ThreadStreamEvent]],
     ) -> AsyncIterator[ActionOutput]:
+        assert action.payload is not None, "Action payload is required"
         if action.type == "sample.show_widget":
             next_state = Index(
                 selected=action.payload.widget,