[Timetable] Exception if no data is available

Environment:


Request Method: GET
Request URL: http://localhost/app/chronos/timetable

Django Version: 2.2.8
Python Version: 3.7.5
Installed Applications:
['django.contrib.admin',
 'django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.messages',
 'django.contrib.staticfiles',
 'django_global_request',
 'settings_context_processor',
 'sass_processor',
 'easyaudit',
 'dbbackup',
 'dbsettings',
 'django_cron',
 'bootstrap4',
 'fa',
 'django_any_js',
 'django_yarnpkg',
 'django_tables2',
 'easy_thumbnails',
 'image_cropping',
 'maintenance_mode',
 'menu_generator',
 'phonenumber_field',
 'debug_toolbar',
 'django_select2',
 'hattori',
 'django_otp.plugins.otp_totp',
 'django_otp.plugins.otp_static',
 'django_otp',
 'otp_yubikey',
 'biscuit.core',
 'impersonate',
 'two_factor',
 'biscuit.apps.alsijil',
 'isbn_field',
 'biscuit.apps.exlibris',
 'biscuit.apps.schild_nrw',
 'biscuit.apps.chronos',
 'biscuit.apps.untis']
Installed Middleware:
['django.middleware.security.SecurityMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.locale.LocaleMiddleware',
 'django_global_request.middleware.GlobalRequestMiddleware',
 'django.middleware.common.CommonMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'debug_toolbar.middleware.DebugToolbarMiddleware',
 'django_otp.middleware.OTPMiddleware',
 'impersonate.middleware.ImpersonateMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware',
 'django.middleware.clickjacking.XFrameOptionsMiddleware',
 'easyaudit.middleware.easyaudit.EasyAuditMiddleware',
 'maintenance_mode.middleware.MaintenanceModeMiddleware']



Traceback:

File "/srv/biscuit/lib/python3.7/site-packages/django/core/handlers/exception.py" in inner
  34.             response = get_response(request)

File "/srv/biscuit/lib/python3.7/site-packages/django/core/handlers/base.py" in _get_response
  115.                 response = self.process_exception_by_middleware(e, request)

File "/srv/biscuit/lib/python3.7/site-packages/django/core/handlers/base.py" in _get_response
  113.                 response = wrapped_callback(request, *callback_args, **callback_kwargs)

File "/usr/lib/python3.7/contextlib.py" in inner
  74.                 return func(*args, **kwds)

File "/srv/biscuit/lib/python3.7/site-packages/django/contrib/auth/decorators.py" in _wrapped_view
  21.                 return view_func(request, *args, **kwargs)

File "/usr/src/BiscuIT-ng/apps/official/BiscuIT-App-Chronos/biscuit/apps/chronos/views.py" in timetable
  58.                              min_max.get('weekday__max', 6) + 1):

Exception Type: TypeError at /app/chronos/timetable
Exception Value: unsupported operand type(s) for +: 'NoneType' and 'int'