#vulnerable code 
                                public String consumeCssIdentifier() {
        StringBuilder accum = new StringBuilder();
        Character c = peek();
        while (!isEmpty() && (Character.isLetterOrDigit(c) || c.equals('-') || c.equals('_'))) {
            accum.append(consume());
            c = peek();
        }
        return accum.toString();
    } 
                            #location 4 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                public String consumeCssIdentifier() {
        int start = pos;
        while (!isEmpty() && (matchesWord() || matchesAny('-', '_')))
            pos++;

        return queue.substring(start, pos);
    }