#vulnerable code 
                                public void testSimpleMapImitation() throws Exception
    {
        MapImitator mapHolder = MAPPER.readValue
            ("{ \"a\" : 3, \"b\" : true }", MapImitator.class);
        Map<String,Object> result = mapHolder._map;
        assertEquals(2, result.size());
        assertEquals(Integer.valueOf(3), result.get("a"));
        assertEquals(Boolean.TRUE, result.get("b"));
    } 
                            #location 5 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                public void testSimpleMapImitation() throws Exception
    {
        MapImitator mapHolder = MAPPER.readValue
            ("{ \"a\" : 3, \"b\" : true, \"c\":[1,2,3] }", MapImitator.class);
        Map<String,Object> result = mapHolder._map;
        assertEquals(3, result.size());
        assertEquals(Integer.valueOf(3), result.get("a"));
        assertEquals(Boolean.TRUE, result.get("b"));
        Object ob = result.get("c");
        assertTrue(ob instanceof List<?>);
        List<?> l = (List<?>)ob;
        assertEquals(3, l.size());
        assertEquals(Integer.valueOf(3), l.get(2));
    }