Error exporting COCO 'DatasetModel not found'

[jsbroks]

Downloading COCO produce error.

Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1813, in full_dispatch_request
    rv = self.dispatch_request()
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 1799, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/usr/local/lib/python3.6/site-packages/flask_restplus/api.py", line 325, in wrapper
    resp = resource(*args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/flask/views.py", line 88, in view
    return self.dispatch_request(*args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/flask_restplus/resource.py", line 44, in dispatch_request
    resp = meth(*args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/flask_login/utils.py", line 261, in decorated_view
    return func(*args, **kwargs)
  File "/workspace/app/api/images.py", line 231, in get
    return coco_util.get_image_coco(image)
  File "/workspace/app/util/coco_util.py", line 93, in get_image_coco
    dataset = DatasetModel.objects(id=image.dataset_id).first()
NameError: name 'DatasetModel' is not defined