edX staging server returning error on API request for certificates

[sentry-io[bot]]

I believe this is a data issue specific to my user, but I'm not sure. We should keep an eye out for this happening to other users in production.

Sentry Issue: MICROMASTERS-3P5

HTTPError: 500 Server Error: Internal Server Error for url: https://courses.stage.edx.org/api/certificates/v0/certificates/pdpinch/courses/MITx/14.73x_1/1T2015/
(1 additional frame(s) were not displayed)
...
  File "dashboard/api_edx_cache.py", line 322, in update_cache_if_expired
    update_func(user, edx_client)
  File "dashboard/api_edx_cache.py", line 236, in update_cached_certificates
    get_social_username(user), course_ids)
  File "edx_api/certificates/__init__.py", line 71, in get_student_certificates
    all_certificates.append(self.get_student_certificate(username, course_id))
  File "edx_api/certificates/__init__.py", line 47, in get_student_certificate
    resp.raise_for_status()
  File "requests/models.py", line 940, in raise_for_status
    raise HTTPError(http_error_msg, response=self)

Impossible to refresh edX cache