@Override
  @SuppressWarnings("UseOfSystemOutOrSystemErr")
  public void warn(String message, @Nullable Throwable t) {
    t = ensureNotControlFlow(t);
    System.err.println("WARN: " + message);
    if (t != null) t.printStackTrace(System.err);
  }
@Override
  @SuppressWarnings("UseOfSystemOutOrSystemErr")
  public void warn(String message, @Nullable Throwable t)