#vulnerable code 
                                @Test
    public void testConfig() {
        final LoggerContext ctx = Configurator.initialize("Test1", "target/test-classes/log4j2-mapfilter.xml");
        final Configuration config = ctx.getConfiguration();
        final Filter filter = config.getFilter();
        assertNotNull("No MapFilter", filter);
        assertTrue("Not a MapFilter", filter instanceof  MapFilter);
        final MapFilter mapFilter = (MapFilter) filter;
        assertFalse("Should not be And filter", mapFilter.isAnd());
        final Map<String, List<String>> map = mapFilter.getMap();
        assertNotNull("No Map", map);
        assertFalse("No elements in Map", map.isEmpty());
        assertEquals("Incorrect number of elements in Map", 1, map.size());
        assertTrue("Map does not contain key eventId", map.containsKey("eventId"));
        assertEquals("List does not contain 2 elements", 2, map.get("eventId").size());
        final Logger logger = LogManager.getLogger(MapFilterTest.class);
        final Map<String, String> eventMap = new HashMap<>();
        eventMap.put("eventId", "Login");
        logger.debug(new MapMessage(eventMap));
        final Appender app = config.getAppender("LIST");
        assertNotNull("No List appender", app);
        final List<String> msgs = ((ListAppender) app).getMessages();
        assertNotNull("No messages", msgs);
        assertFalse("No messages", msgs.isEmpty());


    } 
                            #location 4 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Test
    public void testConfig() {
        final Configuration config = context.getConfiguration();
        final Filter filter = config.getFilter();
        assertNotNull("No MapFilter", filter);
        assertTrue("Not a MapFilter", filter instanceof  MapFilter);
        final MapFilter mapFilter = (MapFilter) filter;
        assertFalse("Should not be And filter", mapFilter.isAnd());
        final Map<String, List<String>> map = mapFilter.getMap();
        assertNotNull("No Map", map);
        assertFalse("No elements in Map", map.isEmpty());
        assertEquals("Incorrect number of elements in Map", 1, map.size());
        assertTrue("Map does not contain key eventId", map.containsKey("eventId"));
        assertEquals("List does not contain 2 elements", 2, map.get("eventId").size());
        final Logger logger = LogManager.getLogger(MapFilterTest.class);
        final Map<String, String> eventMap = new HashMap<>();
        eventMap.put("eventId", "Login");
        logger.debug(new MapMessage(eventMap));
        final ListAppender app = context.getListAppender("LIST");
        final List<String> msgs = app.getMessages();
        assertNotNull("No messages", msgs);
        assertFalse("No messages", msgs.isEmpty());


    }