Update tools/demo_api.py

tools/demo_api.py

@@ -157,7 +157,7 @@ def run_detection(predictor, path):
                      "filename": image_name }
         img_list.append(img_entry)
 
-        if len(outputs[0]):
+        if outputs[0] is not None:
             for id, output in enumerate(outputs[0]):
                 print(output)
                 ann_entry = {"id": id,