fix error code for delete folder (#42470) (#42519)

(cherry picked from commit e13e6a7bd7)

Co-authored-by: ying-jeanne <74549700+ying-jeanne@users.noreply.github.com>

pkg/services/libraryelements/database.go

@@ -692,9 +692,15 @@ func (l *LibraryElementService) deleteLibraryElementsInFolderUID(c context.Conte
 		if err != nil {
 			return err
 		}
+
+		if len(folderUIDs) == 0 {
+			return models.ErrFolderNotFound
+		}
+
 		if len(folderUIDs) != 1 {
 			return fmt.Errorf("found %d folders, while expecting at most one", len(folderUIDs))
 		}
+
 		folderID := folderUIDs[0].ID
 
 		if err := l.requirePermissionsOnFolder(c, signedInUser, folderID); err != nil {

pkg/services/libraryelements/libraryelements_test.go

@@ -65,6 +65,12 @@ func TestDeleteLibraryPanelsInFolder(t *testing.T) {
 			require.EqualError(t, err, ErrFolderHasConnectedLibraryElements.Error())
 		})
 
+	scenarioWithPanel(t, "When an admin tries to delete a folder uid that doesn't exist, it should fail",
+		func(t *testing.T, sc scenarioContext) {
+			err := sc.service.DeleteLibraryElementsInFolder(sc.reqContext.Req.Context(), sc.reqContext.SignedInUser, sc.folder.Uid+"xxxx")
+			require.EqualError(t, err, models.ErrFolderNotFound.Error())
+		})
+
 	scenarioWithPanel(t, "When an admin tries to delete a folder that contains disconnected elements, it should delete all disconnected elements too",
 		func(t *testing.T, sc scenarioContext) {
 			command := getCreateVariableCommand(sc.folder.Id, "query0")