Confusing error if prediction fails

[taw10]

If the server fails to return a valid result, the error message is somewhat confusing:

Connecting to server ...
[]
Received predictions in 0.1577 seconds
Client got all predictions in 0.1583 seconds
Traceback (most recent call last):
  File "./predict.py", line 170, in <module>
    loop_present, r, c, h, w = get_loop_bbox(predictions, min_size=args.min_size)
  File "./predict.py", line 52, in get_loop_bbox
    loop_present, r, c, h, w, r_max, c_max, r_min, c_min, bbox, area, notion_prediction = get_notion_prediction(predictions, ['crystal', 'loop_inside', 'loop'], k=k, min_size=min_size)
  File "./predict.py", line 125, in get_notion_prediction
    notion_mask = get_notion_mask_from_predictions(predictions, notion, k=k, notion_indices=notion_indices, threshold=threshold, min_size=min_size)
  File "./predict.py", line 90, in get_notion_mask_from_predictions
    notion_mask = np.zeros(predictions[0].shape[1:3], dtype=bool)
IndexError: list index out of range

Here, get_predictions was modified as follows:

   22     socket.send(pickle.dumps(request_arguments))                                                     
   23     raw_predictions = socket.recv()                                                                  
   24     predictions = pickle.loads(raw_predictions)                                                      
+  25     print(predictions)                                                                               
   26     if verbose:                                                                                      
   27         print('Received predictions in %.4f seconds' % (time.time() - start))                        
   28     return predictions                                                                               

The real error is that predictions is an empty list (in this case due to a different problem). This should be detected and trapped.