Fix Error 500s creating merge requests with external issue tracker

When JIRA or Redmine were enabled and the branch name did not match the
matching regular expression, the `issue_iid` would be `nil`, preventing
users from creating merge requests.

Closes #43193

1 files changed, 5 insertions, 3 deletions

diff --git a/app/services/merge_requests/build_service.rb b/app/services/merge_requests/build_service.rb
index 2ae855d078b..ab6f8ea44a9 100644
--- a/app/services/merge_requests/build_service.rb
+++ b/app/services/merge_requests/build_service.rb
@@ -160,10 +160,12 @@ module MergeRequests
 
       merge_request.title = "Resolve \"#{issue.title}\"" if issue.is_a?(Issue)
 
-      unless merge_request.title
-        branch_title = source_branch.downcase.remove(issue_iid.downcase).titleize.humanize
+      return if merge_request.title.present?
+
+      if issue_iid.present?
         merge_request.title = "Resolve #{issue_iid}"
-        merge_request.title += " \"#{branch_title}\"" unless branch_title.empty?
+        branch_title = source_branch.downcase.remove(issue_iid.downcase).titleize.humanize
+        merge_request.title += " \"#{branch_title}\"" if branch_title.present?
       end
     end