Fix build_404_handler negotiations bug

[kondratevdev]

I have made things!

Checklist

• I have double checked that there are no unrelated changes in this pull request (old patches, accidental config files, etc)
• I have created at least one test case for the changes I have made
• I have updated the documentation for the changes I have made

Related issues

Closes #656

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (2a3bde8) to head (2531d7d).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #653   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          279       279           
  Lines        11438     11442    +4     
  Branches       380       380           
=========================================
+ Hits         11438     11442    +4     

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