fix: check if userId is null

[am97]

Fixes #6113

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 24.08%. Comparing base (6bdbb85) to head (a123dc8).
Report is 4 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6115      +/-   ##
============================================
- Coverage     29.83%   24.08%   -5.75%     
+ Complexity      912      457     -455     
============================================
  Files           289      247      -42     
  Lines         13768    11534    -2234     
  Branches       2165     2165              
============================================
- Hits           4107     2778    -1329     
+ Misses         9346     8441     -905     
  Partials        315      315              

Flag	Coverage Δ
javascript	15.56% <ø> (ø)
php	59.52% <ø> (+0.01%)	⬆️

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[ChristophWurst]

/backport! to stable4.7

[backportbot]

The backport to stable4.7 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable4.7
git pull origin stable4.7

# Create the new backport branch
git checkout -b backport/6115/stable4.7

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick a123dc80

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/6115/stable4.7

Error: Failed to cherry pick commits: error: no cherry-pick or revert in progress
fatal: cherry-pick failed

---

Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.

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