fix test

pkg/gui/presentation/files_test.go

@@ -129,6 +129,7 @@ M file1
 		s := s
 		t.Run(s.name, func(t *testing.T) {
 			viewModel := filetree.NewCommitFileTreeViewModel(func() []*models.CommitFile { return s.files }, utils.NewDummyLog(), true)
+			viewModel.SetRef(&models.Commit{})
 			viewModel.SetTree()
 			for _, path := range s.collapsedPaths {
 				viewModel.ToggleCollapsed(path)