REFACTOR: Clarify assignment fallback chain

app/services/merge_requests/build_service.rb

@@ -128,8 +128,7 @@ module MergeRequests
     #
     def assign_title_and_description
       assign_title_and_description_from_single_commit
-      assign_title_from_issue if target_project.issues_enabled? || target_project.external_issue_tracker
-
+      merge_request.title ||= title_from_issue if target_project.issues_enabled? || target_project.external_issue_tracker
       merge_request.title ||= source_branch.titleize.humanize
       merge_request.title = wip_title if compare_commits.empty?
 
@@ -159,19 +158,18 @@ module MergeRequests
       merge_request.description ||= commit.description.try(:strip)
     end
 
-    def assign_title_from_issue
+    def title_from_issue
       return unless issue
 
-      merge_request.title ||= "Resolve \"#{issue.title}\"" if issue.is_a?(Issue)
+      return "Resolve \"#{issue.title}\"" if issue.is_a?(Issue)
 
-      return if merge_request.title.present?
       return if issue_iid.blank?
 
       title_parts = ["Resolve #{issue.to_reference}"]
       branch_title = source_branch.downcase.remove(issue_iid.downcase).titleize.humanize
 
       title_parts << "\"#{branch_title}\"" if branch_title.present?
-      merge_request.title = title_parts.join(' ')
+      title_parts.join(' ')
     end
 
     def issue_iid