Raise error when user object is not found.

[jkmarx]

Resolves #3175

• Handles the api error when the anon user is missing. Happens when user does not run fab vm update on a fresh instance.

Notes from issue
"Once project is configured to work with django-guardian, calling syncdb management command would create User instance for anonymous user support (with name of AnonymousUser)." https://django-guardian.readthedocs.io/en/stable/configuration.html?highlight=anon

[codecov]

Codecov Report

Merging #3312 into develop will decrease coverage by 0.87%.
The diff coverage is 37.5%.

@@             Coverage Diff             @@
##           develop    #3312      +/-   ##
===========================================
- Coverage    67.32%   66.44%   -0.88%     
===========================================
  Files          375      375              
  Lines        25472    24648     -824     
  Branches       939      939              
===========================================
- Hits         17149    16378     -771     
+ Misses        8323     8270      -53

Impacted Files	Coverage Δ
refinery/user_files_manager/utils.py	76% <37.5%> (-14.25%)	⬇️
refinery/core/serializers.py	86.66% <0%> (-4.93%)	⬇️
refinery/core/views.py	60% <0%> (-3%)	⬇️
refinery/core/api.py	28.01% <0%> (-1.65%)	⬇️
refinery/core/models.py	81.2% <0%> (-0.65%)	⬇️
refinery/core/test_models.py	99.85% <0%> (-0.03%)	⬇️
refinery/core/test_views.py	100% <0%> (ø)	⬆️
refinery/core/urls.py	100% <0%> (ø)	⬆️

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[hackdna]

Thanks, missing AnonymousUser appears to be the root cause. That was addressed in #1103, so I'll reopen it and move it to the Next milestone.

[hackdna]

Looks good, just one additional item.

[hackdna]

Also, replace the line above with:

from guardian.compat import get_user_model

then:

User = get_user_model()

as described here: https://django-guardian.readthedocs.io/en/latest/configuration.html