!15960 quant_mode raise type error

From: @zhang__sss
Reviewed-by: @zhoufeng54,@zh_qh
Signed-off-by: @zh_qh

mindspore/train/serialization.py

@@ -815,9 +815,11 @@ def quant_mode_manage(func):
     Inherit the quant_mode in old version.
     """
     def warpper(network, *inputs, file_format, **kwargs):
-        if not kwargs.get('quant_mode', None):
+        if 'quant_mode' not in kwargs:
             return network
         quant_mode = kwargs['quant_mode']
+        if not isinstance(quant_mode, str):
+            raise TypeError("The type of quant_mode should be str, but got {}.".format(type(quant_mode)))
         if quant_mode in ('AUTO', 'MANUAL'):
             kwargs['quant_mode'] = 'QUANT'
         return func(network, *inputs, file_format=file_format, **kwargs)