AssertionError: Status must be a string

[gotohx]

I use the image (https://hub.docker.com/r/blemmenes/radosgw_usage_exporter), when I call the interface, some errors occur：

Traceback (most recent call last):
  File "/usr/local/lib/python2.7/wsgiref/handlers.py", line 85, in run
    self.result = application(self.environ, self.start_response)
  File "/usr/local/lib/python2.7/site-packages/prometheus_client/exposition.py", line 125, in prometheus_app
    start_response(status, [header])
  File "/usr/local/lib/python2.7/wsgiref/handlers.py", line 173, in start_response
    assert type(status) is StringType,"Status must be a string"
AssertionError: Status must be a string

My Ceph version is 15.2.17.