Received 500 on export Student Scores

Summary

Received 500 on export Student Scores

Steps to reproduce

Example Project

What is the current bug behavior?

What is the expected correct behavior?

Relevant logs and/or screenshots

AttributeError at /api/export/json/
'NoneType' object has no attribute 'module_reference'

Request Method: POST
Request URL: http://localhost:8000/api/export/json/
Django Version: 2.1.4
Python Executable: /home/robin/code/grady/.venv/bin/python
Python Version: 3.6.2
Python Path: ['/home/robin/code/grady', '/usr/local/lib/python36.zip', '/usr/local/lib/python3.6', '/usr/local/lib/python3.6/lib-dynload', '/home/robin/code/grady/.venv/lib/python3.6/site-packages']
Server time: Thu, 14 Feb 2019 14:50:37 +0000
Installed Applications:
['django.contrib.admin',
 'django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.messages',
 'whitenoise.runserver_nostatic',
 'django.contrib.staticfiles',
 'django_extensions',
 'rest_framework',
 'corsheaders',
 'drf_yasg',
 'core']
Installed Middleware:
['corsheaders.middleware.CorsMiddleware',
 'django.middleware.common.CommonMiddleware',
 'django.middleware.security.SecurityMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.common.CommonMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware',
 'django.middleware.clickjacking.XFrameOptionsMiddleware',
 'whitenoise.middleware.WhiteNoiseMiddleware']


Traceback:

File "/home/robin/code/grady/.venv/lib/python3.6/site-packages/django/core/handlers/exception.py" in inner
  34.             response = get_response(request)

File "/home/robin/code/grady/.venv/lib/python3.6/site-packages/django/core/handlers/base.py" in _get_response
  126.                 response = self.process_exception_by_middleware(e, request)

File "/home/robin/code/grady/.venv/lib/python3.6/site-packages/django/core/handlers/base.py" in _get_response
  124.                 response = wrapped_callback(request, *callback_args, **callback_kwargs)

File "/usr/local/lib/python3.6/contextlib.py" in inner
  52.                 return func(*args, **kwds)

File "/home/robin/code/grady/.venv/lib/python3.6/site-packages/django/views/decorators/csrf.py" in wrapped_view
  54.         return view_func(*args, **kwargs)

File "/home/robin/code/grady/.venv/lib/python3.6/site-packages/django/views/generic/base.py" in view
  68.             return self.dispatch(request, *args, **kwargs)

File "/home/robin/code/grady/.venv/lib/python3.6/site-packages/rest_framework/views.py" in dispatch
  495.             response = self.handle_exception(exc)

File "/home/robin/code/grady/.venv/lib/python3.6/site-packages/rest_framework/views.py" in handle_exception
  455.             self.raise_uncaught_exception(exc)

File "/home/robin/code/grady/.venv/lib/python3.6/site-packages/rest_framework/views.py" in dispatch
  492.             response = handler(request, *args, **kwargs)

File "/home/robin/code/grady/core/views/export.py" in post
  47.             in StudentInfo.get_annotated_score_submission_list()]

File "/home/robin/code/grady/core/views/export.py" in <listcomp>
  46.              } for student

Exception Type: AttributeError at /api/export/json/
Exception Value: 'NoneType' object has no attribute 'module_reference'
Request information:
USER: hundt

Possible fixes