while (true) {
        if (needle == cv) {
          return chars[c - 1];
        } else if ((lv <= needle) && (needle < cv)) {
          return chars[l];
        } else if (needle == rv) {
          return chars[r];
        } else if (needle < cv) {
          rv = cv;
          r = c;
          c = l + (r - l) / 2;
          cv = prob[c];
        } else if (needle == cv) {
          return chars[c];

    /**
     * Assert the property is not null.
     * @param property The value of the property. (NotNull)
     */
    protected void assertPropertyNotNull(String property) {
        if (property == null) {
            String msg = "The argument 'property' for message should not be null.";
            throw new IllegalArgumentException(msg);
        }
    }