!2589 fix checkpoint evaliaction.

Merge pull request !2589 from chenzhongming/fix_ckpt

mindspore/train/serialization.py

@@ -186,9 +186,10 @@ def load_checkpoint(ckpt_file_name, model_type="normal", net=None):
         raise ValueError(e.__str__())
 
     parameter_dict = {}
-    if model_type != checkpoint_list.model_type:
-        raise KeyError("Checkpoint file model type({}) is not equal to input model type({}).".format(
-            checkpoint_list.model_type, model_type))
+    if checkpoint_list.model_type:
+        if model_type != checkpoint_list.model_type:
+            raise KeyError("Checkpoint file model type({}) is not equal to input model type({}).".format(
+                checkpoint_list.model_type, model_type))
     try:
         for element in checkpoint_list.value:
             data = element.tensor.tensor_content