@NotNull
 private static VirtualFile[] filterByReadOnliness(@NotNull VirtualFile[] files) {
   List<VirtualFile> result = new ArrayList<VirtualFile>();
   for (VirtualFile file : files) {
     if (file.isInLocalFileSystem()) {
       result.add(file);
     }
   }
   return VfsUtilCore.toVirtualFileArray(result);
 }