Merge branch 'tor/defect/error-reading-mergerequest-null' into 'master'

Attempt to fix errors reading properties from null `mergeRequest`

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/143103



Merged-by: Simon Knox <simon@gitlab.com>
Approved-by: Lorenz van Herwaarden <lvanherwaarden@gitlab.com>
Approved-by: Simon Knox <simon@gitlab.com>
Co-authored-by: Thomas Randolph <trandolph@gitlab.com>