fix summary default (#483)

opencompass/utils/run.py

@@ -99,7 +99,7 @@ def get_config_from_arg(args) -> Config:
                      run_cfg=dict(num_gpus=args.num_gpus))
         models.append(model)
 
-    summarizer = None
+    summarizer = {}
     if args.summarizer:
         summarizers_dir = os.path.join(args.config_dir, 'summarizers')
         s = match_cfg_file(summarizers_dir, [args.summarizer])[0]