private static @NotNull Set<VirtualFile> union(boolean addDir1, @NotNull VirtualFile dir1, boolean addDir2, @NotNull VirtualFile dir2) {
      if (addDir1 && addDir2) return ContainerUtil.newHashSet(dir1, dir2);
      if (addDir1) return Collections.singleton(dir1);
      if (addDir2) return Collections.singleton(dir2);
      return Collections.emptySet();
    }
private static @NotNull Set<VirtualFile> union(boolean addDir1, @NotNull VirtualFile dir1, boolean addDir2, @NotNull VirtualFile dir2)