UnicodeEscaper e = new PercentEscaper("%", false);
    assertEquals("foo%7Cbar", e.escape("foo|bar"));
    assertEquals("foo%7Cbar", e.escape("foo%7Cbar")); // idempotent
  }

  /** Test that giving a null 'safeChars' string causes a {@link NullPointerException}. */
  public void testBadArguments_null() {
    assertThrows(NullPointerException.class, () -> new PercentEscaper(null, false));
  }

  /**