Unable to add co-matainers to packages

• I have described the bug in complete detail in the Description section.
• I have specified steps in the Reproduction section.
• I have included any logs related to the bug in the Logs section.
• I have included the versions which are affected in the Version(s) section.

Description

Attempting to add a user as a co-maintainer of a package results in an internal server error.

Reproduction

Add a use as a co-maintainer via the Manage Co-Maintainers button on a package page.

Logs

Traceback (most recent call last):
  File "/usr/lib/python3.9/site-packages/uvicorn/protocols/http/h11_impl.py", line 373, in run_asgi
    result = await app(self.scope, self.receive, self.send)
  File "/usr/lib/python3.9/site-packages/uvicorn/middleware/proxy_headers.py", line 75, in __call__
    return await self.app(scope, receive, send)
  File "/usr/lib/python3.9/site-packages/uvicorn/middleware/message_logger.py", line 82, in __call__
    raise exc from None
  File "/usr/lib/python3.9/site-packages/uvicorn/middleware/message_logger.py", line 78, in __call__
    await self.app(scope, inner_receive, inner_send)
  File "/usr/lib/python3.9/site-packages/fastapi/applications.py", line 208, in __call__
    await super().__call__(scope, receive, send)
  File "/usr/lib/python3.9/site-packages/starlette/applications.py", line 112, in __call__
    await self.middleware_stack(scope, receive, send)
  File "/usr/lib/python3.9/site-packages/starlette/middleware/errors.py", line 181, in __call__
    raise exc
  File "/usr/lib/python3.9/site-packages/starlette/middleware/errors.py", line 159, in __call__
    await self.app(scope, receive, _send)
  File "/usr/lib/python3.9/site-packages/starlette/middleware/sessions.py", line 77, in __call__
    await self.app(scope, receive, send_wrapper)
  File "/usr/lib/python3.9/site-packages/starlette/middleware/authentication.py", line 48, in __call__
    await self.app(scope, receive, send)
  File "/usr/lib/python3.9/site-packages/starlette/middleware/base.py", line 63, in __call__
    response = await self.dispatch_func(request, call_next)
  File "/aurweb/./aurweb/asgi.py", line 182, in id_redirect_middleware
    return task.result()
  File "/usr/lib/python3.9/site-packages/starlette/middleware/base.py", line 44, in call_next
    raise app_exc
  File "/usr/lib/python3.9/site-packages/starlette/middleware/base.py", line 34, in coro
    await self.app(scope, request.receive, send_stream.send)
  File "/usr/lib/python3.9/site-packages/starlette/middleware/base.py", line 63, in __call__
    response = await self.dispatch_func(request, call_next)
  File "/aurweb/./aurweb/asgi.py", line 162, in check_terms_of_service
    return task.result()
  File "/usr/lib/python3.9/site-packages/starlette/middleware/base.py", line 44, in call_next
    raise app_exc
  File "/usr/lib/python3.9/site-packages/starlette/middleware/base.py", line 34, in coro
    await self.app(scope, request.receive, send_stream.send)
  File "/usr/lib/python3.9/site-packages/starlette/middleware/base.py", line 63, in __call__
    response = await self.dispatch_func(request, call_next)
  File "/aurweb/./aurweb/asgi.py", line 120, in add_security_headers
    response = response.result()
  File "/usr/lib/python3.9/site-packages/starlette/middleware/base.py", line 44, in call_next
    raise app_exc
  File "/usr/lib/python3.9/site-packages/starlette/middleware/base.py", line 34, in coro
    await self.app(scope, request.receive, send_stream.send)
  File "/usr/lib/python3.9/site-packages/starlette/middleware/base.py", line 63, in __call__
    response = await self.dispatch_func(request, call_next)
  File "/usr/lib/python3.9/site-packages/prometheus_fastapi_instrumentator/instrumentation.py", line 172, in dispatch_middleware
    raise e from None
  File "/usr/lib/python3.9/site-packages/prometheus_fastapi_instrumentator/instrumentation.py", line 169, in dispatch_middleware
    response = await call_next(request)
  File "/usr/lib/python3.9/site-packages/starlette/middleware/base.py", line 44, in call_next
    raise app_exc
  File "/usr/lib/python3.9/site-packages/starlette/middleware/base.py", line 34, in coro
    await self.app(scope, request.receive, send_stream.send)
  File "/usr/lib/python3.9/site-packages/starlette/exceptions.py", line 82, in __call__
    raise exc
  File "/usr/lib/python3.9/site-packages/starlette/exceptions.py", line 71, in __call__
    await self.app(scope, receive, sender)
  File "/usr/lib/python3.9/site-packages/starlette/routing.py", line 656, in __call__
    await route.handle(scope, receive, send)
  File "/usr/lib/python3.9/site-packages/starlette/routing.py", line 259, in handle
    await self.app(scope, receive, send)
  File "/usr/lib/python3.9/site-packages/starlette/routing.py", line 61, in app
    response = await func(request)
  File "/usr/lib/python3.9/site-packages/fastapi/routing.py", line 226, in app
    raw_response = await run_endpoint_function(
  File "/usr/lib/python3.9/site-packages/fastapi/routing.py", line 159, in run_endpoint_function
    return await dependant.call(**values)
  File "/aurweb/./aurweb/auth/__init__.py", line 145, in wrapper
    return await func(request, *args, **kwargs)
  File "/aurweb/./aurweb/routers/packages.py", line 516, in package_base_comaintainers_post
    users.remove(str())  # Remove any empty strings from the set.
KeyError: ''

Version(s)

MPR: https://github.com/makedeb/mprweb/commit/ebfe3e0