DIGITS 4 Object Detection Bounding Boxes Visualization Test ValueError

I am using DIGIT (4 on Ubuntu 14.04) on AWS (https://aws.amazon.com/marketplace/pp/B01LZN28VD).

After I trained an object detection model with custom data, I tried to visualize bounding boxes.
([Select Visualization Method], [Bounding boxes], and [Test One])

But I got ValueError…

ValueError
The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/flask/app.py", line 1475, in full_dispatch_request
    rv = self.dispatch_request()
  File "/usr/lib/python2.7/dist-packages/flask/app.py", line 1461, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/usr/share/digits/digits/webapp.py", line 65, in decorated
    return f(*args, **kwargs)
  File "/usr/share/digits/digits/model/images/generic/views.py", line 343, in infer_one
    outputs)
  File "/usr/share/digits/digits/model/images/generic/views.py", line 592, in get_inference_visualizations
    output_data)
  File "/usr/share/digits/digits/extensions/view/boundingBox/view.py", line 124, in process_data
    if output[-1] > 0:
ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

How can I visualize?