Fix nil user handling in UpdateMirrorService

Closes #605

CHANGELOG-EE

 Please view this file on the master branch, on stable branches it's out of date.
 
 v 8.9.0 (unreleased)
+  - Fix nil user handling in UpdateMirrorService
 
 v 8.8.3
   - Make it clear the license overusage is visible only to admins

app/services/projects/update_mirror_service.rb

@@ -6,7 +6,7 @@ module Projects
     def execute
       return false unless project.mirror?
 
-      unless current_user.can?(:push_code_to_protected_branches, project)
+      unless can?(current_user, :push_code_to_protected_branches, project)
         return error("The mirror user is not allowed to push code to all branches on this project.")
       end
 

spec/services/projects/update_mirror_service_spec.rb

@@ -75,6 +75,16 @@ describe Projects::UpdateMirrorService do
         expect(result[:status]).to eq(:error)
       end
     end
+
+    describe "when no user is present" do
+      let(:mirror_user) { }
+
+      it "fails" do
+        result = subject.execute
+
+        expect(result[:status]).to eq(:error)
+      end
+    end
   end
 
   def fetch_mirror(repository)