Regression in the patches API

[Ralf Ramsauer]

Hi,

it seems that the /patches-API is broken under certain conditions. The
API call throws an exception if the following conditions are met:
  - The user is logged in a browser
  - In the browser, the user requests /api/patches/<someid>/
  - The user is maintainer of the project related to <someid>

This fault can easily be reproduced with a vanilla patchwork instance:
1. ./manage.py createsuperuser # create 'admin' superuser
2. Login in a browser as admin
3. Create some new project
4. ./manage.py parsearchive list.mbox # import some patches
6. In the browser, navigate to /admin/auth/user/1/change
   and add the user as maintainer of the project
7. In the browser, navigate to /api/patches/1
8. Exception is thrown

The exception is not thrown, if step 6 is either skipped or reverted.
Please find the backtrace attached.

Thanks
  Ralf
-------------- next part --------------
web_1  | Internal Server Error: /api/patches/1/
web_1  | Traceback (most recent call last):
web_1  |   File "/opt/pyenv/versions/3.8.2/lib/python3.8/site-packages/django/core/handlers/exception.py", line 34, in inner
web_1  |     response = get_response(request)
web_1  |   File "/opt/pyenv/versions/3.8.2/lib/python3.8/site-packages/django/core/handlers/base.py", line 145, in _get_response
web_1  |     response = self.process_exception_by_middleware(e, request)
web_1  |   File "/opt/pyenv/versions/3.8.2/lib/python3.8/site-packages/django/core/handlers/base.py", line 143, in _get_response
web_1  |     response = response.render()
web_1  |   File "/opt/pyenv/versions/3.8.2/lib/python3.8/site-packages/django/template/response.py", line 105, in render
web_1  |     self.content = self.rendered_content
web_1  |   File "/opt/pyenv/versions/3.8.2/lib/python3.8/site-packages/rest_framework/response.py", line 70, in rendered_content
web_1  |     ret = renderer.render(self.data, accepted_media_type, context)
web_1  |   File "/opt/pyenv/versions/3.8.2/lib/python3.8/site-packages/rest_framework/renderers.py", line 724, in render
web_1  |     context = self.get_context(data, accepted_media_type, renderer_context)
web_1  |   File "/opt/pyenv/versions/3.8.2/lib/python3.8/site-packages/rest_framework/renderers.py", line 695, in get_context
web_1  |     'put_form': self.get_rendered_html_form(data, view, 'PUT', request),
web_1  |   File "/opt/pyenv/versions/3.8.2/lib/python3.8/site-packages/rest_framework/renderers.py", line 511, in get_rendered_html_form
web_1  |     return self.render_form_for_serializer(serializer)
web_1  |   File "/opt/pyenv/versions/3.8.2/lib/python3.8/site-packages/rest_framework/renderers.py", line 518, in render_form_for_serializer
web_1  |     return form_renderer.render(
web_1  |   File "/opt/pyenv/versions/3.8.2/lib/python3.8/site-packages/rest_framework/renderers.py", line 372, in render
web_1  |     return template.render(context)
web_1  |   File "/opt/pyenv/versions/3.8.2/lib/python3.8/site-packages/django/template/backends/django.py", line 61, in render
web_1  |     return self.template.render(context)
web_1  |   File "/opt/pyenv/versions/3.8.2/lib/python3.8/site-packages/django/template/base.py", line 171, in render
web_1  |     return self._render(context)
web_1  |   File "/opt/pyenv/versions/3.8.2/lib/python3.8/site-packages/django/test/utils.py", line 95, in instrumented_test_render
web_1  |     return self.nodelist.render(context)
web_1  |   File "/opt/pyenv/versions/3.8.2/lib/python3.8/site-packages/django/template/base.py", line 936, in render
web_1  |     bit = node.render_annotated(context)
web_1  |   File "/opt/pyenv/versions/3.8.2/lib/python3.8/site-packages/django/template/base.py", line 903, in render_annotated
web_1  |     return self.render(context)
web_1  |   File "/opt/pyenv/versions/3.8.2/lib/python3.8/site-packages/django/template/defaulttags.py", line 209, in render
web_1  |     nodelist.append(node.render_annotated(context))
web_1  |   File "/opt/pyenv/versions/3.8.2/lib/python3.8/site-packages/django/template/base.py", line 903, in render_annotated
web_1  |     return self.render(context)
web_1  |   File "/opt/pyenv/versions/3.8.2/lib/python3.8/site-packages/django/template/defaulttags.py", line 309, in render
web_1  |     return nodelist.render(context)
web_1  |   File "/opt/pyenv/versions/3.8.2/lib/python3.8/site-packages/django/template/base.py", line 936, in render
web_1  |     bit = node.render_annotated(context)
web_1  |   File "/opt/pyenv/versions/3.8.2/lib/python3.8/site-packages/django/template/base.py", line 903, in render_annotated
web_1  |     return self.render(context)
web_1  |   File "/opt/pyenv/versions/3.8.2/lib/python3.8/site-packages/django/template/library.py", line 192, in render
web_1  |     output = self.func(*resolved_args, **resolved_kwargs)
web_1  |   File "/opt/pyenv/versions/3.8.2/lib/python3.8/site-packages/rest_framework/templatetags/rest_framework.py", line 87, in render_field
web_1  |     return renderer.render_field(field, style)
web_1  |   File "/opt/pyenv/versions/3.8.2/lib/python3.8/site-packages/rest_framework/renderers.py", line 339, in render_field
web_1  |     field = field.as_form_field()
web_1  |   File "/opt/pyenv/versions/3.8.2/lib/python3.8/site-packages/rest_framework/utils/serializer_helpers.py", line 122, in as_form_field
web_1  |     for key, value in self.value.items():
web_1  | AttributeError: 'list' object has no attribute 'items'
web_1  | "GET /api/patches/1/ HTTP/1.1" 500 235336