SonarCloud rightfully says:
  The length of "values" is always ">=0", so update this test to either "==0" or ">0".

        // make sure at least one value was returned
        if(values.length < 0) { // <--- here
            throw new InvalidAttributeValueException("no values for " +
                                                     "attribute \"" +
                                                     tagName + "\"");
        }

There is a subsequent access to values[0], which means the failure would throw AIOOB, not InvalidAttributeValueException.