#fixed code
                                private void parseStartTag() {
        tq.consume("<");
        Attributes attributes = new Attributes();

        String tagName = tq.consumeWord();
        while (!tq.matchesAny("<", "/>", ">") && !tq.isEmpty()) {
            Attribute attribute = parseAttribute();
            if (attribute != null)
                attributes.put(attribute);
        }

        Tag tag = Tag.valueOf(tagName);
        StartTag startTag = new StartTag(tag, attributes);
        Element child = new Element(startTag);

        boolean emptyTag;
        if (tq.matchChomp("/>")) { // empty tag, don't add to stack
            emptyTag = true;
        } else {
            tq.matchChomp(">"); // safe because checked above (or ran out of data)
            emptyTag = false;
        }

        // pc data only tags (textarea, script): chomp to end tag, add content as text node
        if (tag.isData()) {
            String data = tq.chompTo("</" + tagName);
            tq.chompTo(">");
            TextNode textNode = TextNode.createFromEncoded(data); // TODO: maybe have this be another data type? So doesn't come back in text()?
            child.addChild(textNode);

            if (tag.equals(titleTag))
                doc.setTitle(child.text());
        }

        // switch between html, head, body, to preserve doc structure
        if (tag.equals(htmlTag)) {
            doc.getAttributes().mergeAttributes(attributes);
        } else if (tag.equals(headTag)) {
            doc.getHead().getAttributes().mergeAttributes(attributes);
            // head is on stack from start, no action required
        } else if (last().getTag().equals(headTag) && !headTag.canContain(tag)) {
            // switch to body
            stack.removeLast();
            stack.addLast(doc.getBody());
            last().addChild(child);
            if (!emptyTag)
                stack.addLast(child);
        } else if (tag.equals(bodyTag) && last().getTag().equals(htmlTag)) {
            doc.getBody().getAttributes().mergeAttributes(attributes);
            stack.removeLast();
            stack.addLast(doc.getBody());
        } else {
            Element parent = popStackToSuitableContainer(tag);
            parent.addChild(child);
            if (!emptyTag && !tag.isData()) // TODO: only check for data here because last() == head is wrong; should be ancestor is head
                stack.addLast(child);
        }
    }
#vulnerable code 
                                private void parseStartTag() {
        tq.consume("<");
        Attributes attributes = new Attributes();

        String tagName = tq.consumeWord();
        while (!tq.matches("<") && !tq.matches("/>") && !tq.matches(">") && !tq.isEmpty()) {
            Attribute attribute = parseAttribute();
            if (attribute != null)
                attributes.put(attribute);
        }

        Tag tag = Tag.valueOf(tagName);
        StartTag startTag = new StartTag(tag, attributes);
        Element child = new Element(startTag);

        boolean emptyTag;
        if (tq.matchChomp("/>")) { // empty tag, don't add to stack
            emptyTag = true;
        } else {
            tq.matchChomp(">"); // safe because checked above (or ran out of data)
            emptyTag = false;
        }

        // pc data only tags (textarea, script): chomp to end tag, add content as text node
        if (tag.isData()) {
            String data = tq.chompTo("</" + tagName);
            tq.chompTo(">");
            TextNode textNode = TextNode.createFromEncoded(data);
            child.addChild(textNode);

            if (tag.equals(titleTag))
                doc.setTitle(child.text());
        }

        // switch between html, head, body, to preserve doc structure
        if (tag.equals(htmlTag)) {
            doc.getAttributes().mergeAttributes(attributes);
        } else if (tag.equals(headTag)) {
            doc.getHead().getAttributes().mergeAttributes(attributes);
            // head is on stack from start, no action required
        } else if (last().getTag().equals(headTag) && !headTag.canContain(tag)) {
            // switch to body
            stack.removeLast();
            stack.addLast(doc.getBody());
            last().addChild(child);
            if (!emptyTag)
                stack.addLast(child);
        } else if (tag.equals(bodyTag) && last().getTag().equals(htmlTag)) {
            doc.getBody().getAttributes().mergeAttributes(attributes);
            stack.removeLast();
            stack.addLast(doc.getBody());
        } else {
            Element parent = popStackToSuitableContainer(tag);
            parent.addChild(child);
            if (!emptyTag && !tag.isData()) // TODO: only check for data here because last() == head is wrong; should be ancestor is head
                stack.addLast(child);
        }
    } 
                            #location 54 
                            #vulnerability type NULL_DEREFERENCE