@Udf(description = "Returns a masked version of the input string. All characters except for the"
      + " last n will be replaced according to the default masking rules.")
  @SuppressWarnings("MethodMayBeStatic") // Invoked via reflection
  public String mask(
      @UdfParameter("input STRING to be masked") final String input,
      @UdfParameter("number of characters to keep unmasked at the end") final int numChars
  ) {
    return doMask(new Masker(), input, numChars);
  }
@Test
  public void shouldMaskOnlySpecifiedCharTypes() {
    final String result = udf.mask("AbCd#$123xy Z", 5, null, "q", null, "=");
    assertThat(result, is("AqCq==123xy Z"));
  }