[Dygraph]fix problems in export_model.py (#1932)

* fix problems in export_model.py

* modify code

tools/export_model.py

@@ -57,8 +57,10 @@ def parse_args():
 def dygraph_to_static(model, save_dir, cfg):
     if not os.path.exists(save_dir):
         os.makedirs(save_dir)
+    image_shape = None
+    if 'inputs_def' in cfg['TestReader']:
         inputs_def = cfg['TestReader']['inputs_def']
-    image_shape = inputs_def.get('image_shape')
+        image_shape = inputs_def.get('image_shape', None)
     if image_shape is None:
         image_shape = [3, None, None]
     # Save infer cfg
@@ -102,7 +104,7 @@ def main():
 
     cfg = load_config(FLAGS.config)
     # TODO: to be refined in the future
-    if cfg.norm_type == 'sync_bn':
+    if 'norm_type' in cfg and cfg['norm_type'] == 'sync_bn':
         FLAGS.opt['norm_type'] = 'bn'
     merge_config(FLAGS.opt)
     check_config(cfg)