private static void addRecursively(@NotNull Collection<? super VirtualFile> container, @NotNull VirtualFile fromDirectory, @Nullable FileType fileType) {
    VfsUtilCore.visitChildrenRecursively(fromDirectory, new VirtualFileVisitor<Void>(VirtualFileVisitor.SKIP_ROOT) {
      @Override
      public boolean visitFile(@NotNull VirtualFile child) {
        if (!child.isDirectory() && (fileType == null || FileTypeRegistry.getInstance().isFileOfType(child, fileType))) {
          container.add(child);
        }
        return true;
      }
    });
  }
private static void addRecursively(@NotNull Collection<? super VirtualFile> container, @NotNull VirtualFile fromDirectory, @Nullable FileType fileType)