Page crashes because of uploaded avatar

Found a bug? Please fill out the sections below. 👍

Issue Summary

ERROR 2019-10-27 17:38:29,831 log 9 139971433467208 Internal Server Error: /blog/re-using-existing-ssh-keys-on-google-cloud/
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/site-packages/django/core/handlers/exception.py", line 34, in inner
    response = get_response(request)
  File "/usr/local/lib/python3.7/site-packages/django/core/handlers/base.py", line 115, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "/usr/local/lib/python3.7/site-packages/django/core/handlers/base.py", line 113, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/usr/local/lib/python3.7/contextlib.py", line 74, in inner
    return func(*args, **kwds)
  File "/usr/local/lib/python3.7/site-packages/wagtail/core/views.py", line 24, in serve
    return page.serve(request, *args, **kwargs)
  File "/usr/local/lib/python3.7/site-packages/wagtail/core/models.py", line 721, in serve
    self.get_context(request, *args, **kwargs)
  File "/usr/local/lib/python3.7/site-packages/wagtail_code_blog/models.py", line 71, in get_context
    raise ex
  File "/usr/local/lib/python3.7/site-packages/wagtail_code_blog/models.py", line 66, in get_context
    ctx["author_image"] = self.owner.wagtail_userprofile.avatar.url
  File "/usr/local/lib/python3.7/site-packages/django/db/models/fields/files.py", line 62, in url
    return self.storage.url(self.name)
  File "/usr/local/lib/python3.7/site-packages/django/contrib/staticfiles/storage.py", line 153, in url
    return self._url(self.stored_name, name, force)
  File "/usr/local/lib/python3.7/site-packages/django/contrib/staticfiles/storage.py", line 132, in _url
    hashed_name = hashed_name_func(*args)
  File "/usr/local/lib/python3.7/site-packages/django/contrib/staticfiles/storage.py", line 420, in stored_name
    raise ValueError("Missing staticfiles manifest entry for '%s'" % clean_name)
ValueError: Missing staticfiles manifest entry for 'avatar_images/avatar_ba71bc28-d8cc-483e-906f-dfb9cc390330_dani_image_rounded.JPG'

Steps to Reproduce

1. (for example) Start a new project with wagtail start myproject
2. Edit models.py as follows…
3. …

Any other relevant information. For example, why do you consider this a bug and what did you expect to happen instead?

• I have confirmed that this issue can be reproduced as described on a fresh Wagtail project: (yes / no)

Technical details

• Python version: 3.7
• Django version: 2.2.4
• Wagtail version: 2.6.2 all the way to git master
• Browser version: all browsers

[gasman]

ManifestFilesMixin does not make sense for media file storage, because it relies on running collectstatic to build a manifest file (and that isn’t going to happen every time you upload a file.)

[danihodovic]

My bad, thank you for saving me hours @gasman !