make better error handling

server.py

@@ -96,13 +96,14 @@ class SegmenterBackground():
 
         results, class_names = self.predict_image(raw_image)
         
-        masks = [results[0].masks.data[i].cpu().numpy() for i in range(len(results[0].masks.data))]
-
-        if len(masks)==0:
+        if len(results[0].masks.data)==0:
             return ("No thing in image") ,0 # 0 error happened ,if so it's 2 returns ,first is message
         
         #----------> other methods
         
+        masks = [results[0].masks.data[i].cpu().numpy() for i in range(len(results[0].masks.data))]
+
+        
         ##### put masks on image
         outpt = self.putMaskImage(raw_image,masks,background_image,blur_radius)