@NotNull
  private static String toString(@NotNull Map<VcsRoot, Set<FilePath>> filesByVcs) {
    return StringUtil.join(filesByVcs.keySet(), vcs
      -> vcs.getVcs() + ": " + StringUtil.join(filesByVcs.get(vcs), path -> path.getPath(), "\n"), "\n");
  }
@NotNull
  private static String toString(@NotNull Map<VcsRoot, Set<FilePath>> filesByVcs)