static int getMaskCharacter(final String mask) {
    if (mask == null) {
      return NO_MASK;
    }

    if (mask.length() != 1) {
      throw new KsqlException("Invalid mask character. "
          + "Must be only single character, but was '" + mask + "'");
    }

    return  mask.codePointAt(0);
  }
@Test(expected = KsqlException.class)
  public void shouldThrowOnMultiCharMask() {
    Masker.getMaskCharacter("2c");
  }