Fix background.go panic when cachedRepo is nil (#332)

* fix background.go panic when cachedRepo is nil

* Add unit test to cover repository refresh when cachedRepo is nil

Author: kushnaidu

pkg/registry/porch/background.go

@@ -195,10 +195,13 @@ func (b *background) handleRepositoryEvent(ctx context.Context, repo *configapi.
 	case watch.Deleted:
 		err = b.cache.CloseRepository(listCtx, repo, repoList.Items)
 	case watch.Modified:
-		if cachedRepo, err := b.cacheRepository(listCtx, repo); err == nil {
+		cachedRepo, err := b.cacheRepository(listCtx, repo)
+		if err == nil && cachedRepo != nil {
 			if err = cachedRepo.Refresh(ctx); err != nil {
 				klog.Warningf("Background repository refresh failed for repo %q: %v", repo.Name, err)
 			}
+		} else {
+			klog.Warningf("cacheRepository failed or returned nil for repo %q: err=%v", repo.Name, err)
 		}
 	default:
 		_, err = b.cacheRepository(listCtx, repo)

pkg/registry/porch/background_test.go

@@ -121,6 +121,17 @@ func TestBackground_HandleRepositoryEvent(t *testing.T) {
 				mockResourceWriter.On("Update", mock.Anything, mock.Anything).Return(nil)
 			},
 		},
+		{
+			name:  "Modified event with nil cachedRepo and no error",
+			event: watch.Modified,
+			setupMocks: func(mockClient *mockclient.MockWithWatch, mockResourceWriter *mockclient.MockSubResourceWriter,
+				mockCache *mockcache.MockCache, mockRepo *mockrepo.MockRepository) {
+				mockClient.On("List", mock.Anything, mock.Anything).Return(nil)
+				mockCache.On("OpenRepository", mock.Anything, mock.AnythingOfType("*v1alpha1.Repository")).Return(nil, nil)
+				mockClient.On("Status").Return(mockResourceWriter)
+				mockResourceWriter.On("Update", mock.Anything, mock.Anything).Return(nil)
+			},
+		},
 		{
 			name:  "Unsuccessful repository deletion event",
 			event: watch.Deleted,