Handle error when foreign user is not found

[Pierre-Gilles]

Pull Request check-list

To ensure your Pull Request can be accepted as fast as possible, make sure to review and check all of these items:

• If your changes affects code, did your write the tests?
• Are tests passing? (npm test on both front/server)
• Is the linter passing? (npm run eslint on both front/server)
• Did you run prettier? (npm run prettier on both front/server)
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Description of change

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[codecov]

Codecov Report

Merging #515 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #515   +/-   ##
=======================================
  Coverage   91.28%   91.28%           
=======================================
  Files         342      342           
  Lines        3869     3869           
=======================================
  Hits         3532     3532           
  Misses        337      337

Flag	Coverage Δ
#server	91.28% <ø> (ø)	⬆️

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