crash on a tags without href

[DetachHead]

<!-- ./docs/index.md -->
<a name="asdf"></a>

mkdocs build

ERROR   -  Error reading page 'configuration/config-files.md': 'href'
Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "C:\Users\user\project\.venv\Scripts\mkdocs.EXE\__main__.py", line 7, in <module>
  File "C:\Users\user\project\.venv\Lib\site-packages\click\core.py", line 1157, in __call__
    return self.main(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\user\project\.venv\Lib\site-packages\click\core.py", line 1078, in main
    rv = self.invoke(ctx)
         ^^^^^^^^^^^^^^^^
  File "C:\Users\user\project\.venv\Lib\site-packages\click\core.py", line 1688, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\user\project\.venv\Lib\site-packages\click\core.py", line 1434, in invoke
    return ctx.invoke(self.callback, **ctx.params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\user\project\.venv\Lib\site-packages\click\core.py", line 783, in invoke
    return __callback(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\user\project\.venv\Lib\site-packages\mkdocs\__main__.py", line 288, in build_command
    build.build(cfg, dirty=not clean)
  File "C:\Users\user\project\.venv\Lib\site-packages\mkdocs\commands\build.py", line 310, in build
    _populate_page(file.page, config, files, dirty)
  File "C:\Users\user\project\.venv\Lib\site-packages\mkdocs\commands\build.py", line 171, in _populate_page
    page.content = config.plugins.on_page_content(
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\user\project\.venv\Lib\site-packages\mkdocs\plugins.py", line 638, in on_page_content
    return self.run_event('page_content', html, page=page, config=config, files=files)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\user\project\.venv\Lib\site-packages\mkdocs\plugins.py", line 566, in run_event
    result = method(item, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\user\project\.venv\Lib\site-packages\mkdocs_unused_files\plugin.py", line 70, in on_page_content
    ref_list.append(self._rewrite_ref(a['href'], page.file.dest_uri))
                                      ~^^^^^^^^
  File "C:\Users\user\project\.venv\Lib\site-packages\bs4\element.py", line 1573, in __getitem__
    return self.attrs[key]
           ~~~~~~~~~~^^^^^
KeyError: 'href'