diff --git a/mlrun/api/schemas/schedule.py b/mlrun/api/schemas/schedule.py
index 0158a0c49d6..08a6df5822d 100644
--- a/mlrun/api/schemas/schedule.py
+++ b/mlrun/api/schemas/schedule.py
@@ -36,8 +36,8 @@ class ScheduleCronTrigger(BaseModel):
     hour: Optional[Union[int, str]]
     minute: Optional[Union[int, str]]
     second: Optional[Union[int, str]]
-    start_date: Optional[Union[datetime, str]]
-    end_date: Optional[Union[datetime, str]]
+    start_date: Union[datetime, str] = None
+    end_date: Union[datetime, str] = None
 
     # APScheduler also supports datetime.tzinfo type, but Pydantic doesn't - so we don't
     timezone: Optional[str]