HTTP Error 500 from KeyError when image lacks src attribute

[PeterNerlich]

Describe the Bug

When checking the src value for images in pages that were just saved, the server assumes that this attribute exists. This is not necessarily the case.

Steps to Reproduce

1. Go to any page of any region or go to create a new one
2. Change the editor from WYSIWYG to HTML by clicking on the View menu and select Source view
3. Paste in <img>
4. Click on Update
5. See error

Expected Behavior

The page form view loads again, and maybe displays a hint that there are empty images

Actual Behavior

The server encounters an uncaught KeyError

Additional Information

Traceback

Apr 02 16:03:53 ERROR django.request - 500 Internal Server Error: /augsburg/pages/de/1/edit/
Traceback (most recent call last):
  File "integreat-cms/.venv/lib/python3.11/site-packages/django/core/handlers/exception.py", line 55, in inner
    response = get_response(request)
               ^^^^^^^^^^^^^^^^^^^^^
  File "integreat-cms/.venv/lib/python3.11/site-packages/django/core/handlers/base.py", line 197, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "integreat-cms/.venv/lib/python3.11/site-packages/django/views/generic/base.py", line 104, in view
    return self.dispatch(request, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "integreat-cms/.venv/lib/python3.11/site-packages/django/utils/decorators.py", line 46, in _wrapper
    return bound_method(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "integreat-cms/.venv/lib/python3.11/site-packages/django/contrib/auth/decorators.py", line 23, in _wrapper_view
    return view_func(request, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "integreat-cms/.venv/lib/python3.11/site-packages/django/views/generic/base.py", line 143, in dispatch
    return handler(request, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "integreat-cms/integreat_cms/cms/utils/tree_mutex.py", line 117, in innermost_function
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "integreat-cms/integreat_cms/cms/views/pages/page_form_view.py", line 305, in post
    if not page_form.is_valid() or not page_translation_form.is_valid():
                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "integreat-cms/.venv/lib/python3.11/site-packages/django/forms/forms.py", line 201, in is_valid
    return self.is_bound and not self.errors
                                 ^^^^^^^^^^^
  File "integreat-cms/.venv/lib/python3.11/site-packages/django/forms/forms.py", line 196, in errors
    self.full_clean()
  File "integreat-cms/.venv/lib/python3.11/site-packages/django/forms/forms.py", line 433, in full_clean
    self._clean_fields()
  File "integreat-cms/.venv/lib/python3.11/site-packages/django/forms/forms.py", line 448, in _clean_fields
    value = getattr(self, "clean_%s" % name)()
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "integreat-cms/integreat_cms/cms/forms/custom_content_model_form.py", line 178, in clean_content
    "Image tag found in content (src: %s)", image.attrib["src"]
                                            ~~~~~~~~~~~~^^^^^^^
  File "src/lxml/etree.pyx", line 2502, in lxml.etree._Attrib.__getitem__
KeyError: 'src'
Apr 02 16:03:53 ERROR django.server - "POST /augsburg/pages/de/1/edit/ HTTP/1.1" 500 20360

[MizukiTemma]

@PeterNerlich I'm thinking what kind of hint message should be shown to users.

Many of them probably don't know what an tag is and how it should look like. Then it probably doesn't help to say "The text contains a broken tag. Please check it" or somehting like that if they don't know how to fix it 😓

But the content cannot be saved as long as there is an broken img tag 🤔 Should we remove broken tags, save the content and tell users, for example, "Did you try to insert an image? Something went wrong. The page/location/event was saved without it. Please try again."

[PeterNerlich]

it probably doesn't help to say "The text contains a broken tag. Please check it" or somehting like that if they don't know how to fix it 😓

It is not anything else than images, right? And an image without a source should be allowed by the HTML spec, AFAIK. Can we just skip the image tag for media checking if the source is missing to prevent the issue and display a message that an image might be broken?