Build noteables in AutocompleteSourcesController#target

app/controllers/projects/autocomplete_sources_controller.rb

@@ -34,9 +34,9 @@ class Projects::AutocompleteSourcesController < Projects::ApplicationController
   def target
     case params[:type]&.downcase
     when 'issue'
-      IssuesFinder.new(current_user, project_id: @project.id).find_by(iid: params[:type_id])
+      IssuesFinder.new(current_user, project_id: @project.id).find_by(iid: params[:type_id]) || @project.issues.build
     when 'mergerequest'
-      MergeRequestsFinder.new(current_user, project_id: @project.id).find_by(iid: params[:type_id])
+      MergeRequestsFinder.new(current_user, project_id: @project.id).find_by(iid: params[:type_id]) || @project.merge_requests.build
     when 'commit'
       @project.commit(params[:type_id])
     end

app/services/projects/autocomplete_service.rb

@@ -47,15 +47,7 @@ module Projects
     end
 
     def commands(noteable, type)
-      noteable ||=
-        case type
-        when 'Issue'
-          @project.issues.build
-        when 'MergeRequest'
-          @project.merge_requests.build
-        end
-
-      return [] unless noteable&.is_a?(Issuable)
+      return [] unless noteable
 
       QuickActions::InterpretService.new(project, current_user).available_commands(noteable)
     end