I spent some time reviewing and researching the specification. It also says

   The server is not required to create meta-variables for all the
   header fields that it receives.  

And this in issue, open since 2010, we have issue two different set of variables one from Apache and from Nginx. So, it Is not certain if http.server should be alinged it any or all, and plus if anything is required.

The discussion on QUERY_STRING was noted, but as Pierre pointed out it was set too

        for k in ('QUERY_STRING', 'REMOTE_HOST', 'CONTENT_LENGTH',
                  'HTTP_USER_AGENT', 'HTTP_COOKIE', 'HTTP_REFERER'):
            env.setdefault(k, "")

For cosmetic purpose, I could remove the existing if condition - https://github.com/python/cpython/pull/23604

I am not sure if we need to add other variables with an empty string value for any reason. 

As a maintainer, I think, we should close this issue.

If there is a bug report, like issue5054, then that is a valid issue, and we should fix it.  If there any specific issues raised with parsing or lack of "required" meta variable that caused the application to break, even that could be fixed.

I am closing this issue with a cosmetic change that stemmed out from the discussion - https://github.com/python/cpython/pull/23604