#vulnerable code 
                                public void testPrefixedUnwrapping() throws Exception
    {
        PrefixUnwrap bean = mapper.readValue("{\"name\":\"Axel\",\"_x\":4,\"_y\":7}", PrefixUnwrap.class);
        assertNotNull(bean);
        assertEquals("Axel", bean.name);
        assertNotNull(bean.location);
        assertEquals(4, bean.location.x);
        assertEquals(7, bean.location.y);
    } 
                            #location 5 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                public void testPrefixedUnwrapping() throws Exception
    {
        PrefixUnwrap bean = MAPPER.readValue("{\"name\":\"Axel\",\"_x\":4,\"_y\":7}", PrefixUnwrap.class);
        assertNotNull(bean);
        assertEquals("Axel", bean.name);
        assertNotNull(bean.location);
        assertEquals(4, bean.location.x);
        assertEquals(7, bean.location.y);
    }