#vulnerable code 
                                @Test
    public void testNextElementSiblings() {
        Document doc = Jsoup.parse("<li id='a'>a</li>" +
            "<li id='b'>b</li>" +
            "<li id='c'>c</li>");
        Element element = doc.getElementById("a");
        List<Element> elementSiblings = element.nextElementSiblings();
        assertNotNull(elementSiblings);
        assertEquals(2, elementSiblings.size());

        Element element1 = doc.getElementById("c");
        List<Element> elementSiblings1 = element1.nextElementSiblings();
        assertNull(elementSiblings1);
    } 
                            #location 12 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Test
    public void testNextElementSiblings() {
        Document doc = Jsoup.parse("<ul id='ul'>" +
            "<li id='a'>a</li>" +
            "<li id='b'>b</li>" +
            "<li id='c'>c</li>" +
            "</ul>" +
            "<div id='div'>" +
            "<li id='d'>d</li>" +
            "</div>");

        Element element = doc.getElementById("a");
        List<Element> elementSiblings = element.nextElementSiblings();
        assertNotNull(elementSiblings);
        assertEquals(2, elementSiblings.size());
        assertEquals("b", elementSiblings.get(0).id());
        assertEquals("c", elementSiblings.get(1).id());

        Element element1 = doc.getElementById("b");
        List<Element> elementSiblings1 = element1.nextElementSiblings();
        assertNotNull(elementSiblings1);
        assertEquals(1, elementSiblings1.size());
        assertEquals("c", elementSiblings1.get(0).id());

        Element element2 = doc.getElementById("c");
        List<Element> elementSiblings2 = element2.nextElementSiblings();
        assertEquals(0, elementSiblings2.size());

        Element ul = doc.getElementById("ul");
        List<Element> elementSiblings3 = ul.nextElementSiblings();
        assertNotNull(elementSiblings3);
        assertEquals(1, elementSiblings3.size());
        assertEquals("div", elementSiblings3.get(0).id());

        Element div = doc.getElementById("div");
        List<Element> elementSiblings4 = div.nextElementSiblings();
        try {
            Element elementSibling = elementSiblings4.get(0);
            fail("This element should has no next siblings");
        } catch (IndexOutOfBoundsException e) {
        }
    }