[UserRepositoryMock] Fix Update error when no user found

[imnasnainaec]

This change is 

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.02%. Comparing base (ae4f84a) to head (50b61bc).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3840   +/-   ##
=======================================
  Coverage   73.02%   73.02%           
=======================================
  Files         286      286           
  Lines       10758    10758           
  Branches     1340     1340           
=======================================
  Hits         7856     7856           
  Misses       2502     2502           
  Partials      400      400           

Flag	Coverage Δ
backend	82.15% <ø> (ø)
frontend	65.87% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[megahirt]

LGTM