*/
  public PercentEscaper(String safeChars, boolean plusForSpace) {
    // TODO(dbeaumont): Switch to static factory methods for creation now that class is final.
    // TODO(dbeaumont): Support escapers where alphanumeric chars are not safe.
    checkNotNull(safeChars); // eager for GWT.
    // Avoid any misunderstandings about the behavior of this escaper
    if (safeChars.matches(".*[0-9A-Za-z].*")) {

    assertThat(escaper.escape("\tFish & Chips\n")).isEqualTo("<tab>Fish <and> Chips<newline>");

    // Verify that everything else is left unescaped.
    String safeChars = "\0\u0100\uD800\uDC00\uFFFF";
    assertThat(escaper.escape(safeChars)).isEqualTo(safeChars);

    // Ensure that Unicode escapers behave correctly wrt badly formed input.
    String badUnicode = "\uDC00\uD800";

    assertThat(e.escape("foo|bar")).isEqualTo("foo%7Cbar");
    assertThat(e.escape("foo%7Cbar")).isEqualTo("foo%7Cbar"); // idempotent
  }

  /** Test that giving a null 'safeChars' string causes a {@link NullPointerException}. */
  @SuppressWarnings("nullness") // test of a bogus call
  public void testBadArguments_null() {

    assertThat(e.escape("foo|bar")).isEqualTo("foo%7Cbar");
    assertThat(e.escape("foo%7Cbar")).isEqualTo("foo%7Cbar"); // idempotent
  }

  /** Test that giving a null 'safeChars' string causes a {@link NullPointerException}. */
  @SuppressWarnings("nullness") // test of a bogus call
  public void testBadArguments_null() {