fix

Author: Jintao-Huang

swift/trainers/mixin.py

@@ -988,7 +988,8 @@ def create_optimizer_and_scheduler(self, num_training_steps: int):
 
     def create_optimizer(self):
         self.optimizer = self.optimizer_callback.create_optimizer()
-        self.optimizer.param_groups = [pg for pg in self.optimizer.param_groups if len(pg['params']) > 0]
+        if self.optimizer is not None:
+            self.optimizer.param_groups = [pg for pg in self.optimizer.param_groups if len(pg['params']) > 0]
         return self.optimizer
 
     def create_scheduler(self, num_training_steps: int, optimizer):