set default flow base schedule

Author: hlky

src/diffusers/schedulers/schedules/flow_schedule.py

@@ -124,7 +124,7 @@ def __init__(
 
     def set_base_schedule(self, base_schedule: Union[str]):
         if base_schedule is None:
-            raise ValueError("Must set base schedule.")
+            base_schedule = self.base_schedules["FlowMatchSD3"]
         if isinstance(base_schedule, str):
             if base_schedule not in self.base_schedules:
                 raise ValueError(f"Expected one of {self.base_schedules.keys()}")