#vulnerable code 
                                @Test
    public void testThresholds() {
        RegexFilter filter = RegexFilter.createFilter(Pattern.compile(".* test .*"), false, null, null);
        filter.start();
        assertTrue(filter.isStarted());
        assertSame(Filter.Result.NEUTRAL,
            filter.filter(null, Level.DEBUG, null, "This is a test message", (Throwable) null));
        assertSame(Filter.Result.DENY, filter.filter(null, Level.ERROR, null, "This is not a test", (Throwable) null));
        LogEvent event = new Log4jLogEvent(null, null, null, Level.DEBUG, new SimpleMessage("Another test message"), null);
        assertSame(Filter.Result.NEUTRAL, filter.filter(event));
        event = new Log4jLogEvent(null, null, null, Level.ERROR, new SimpleMessage("test"), null);
        assertSame(Filter.Result.DENY, filter.filter(event));
        filter = RegexFilter.createFilter((Pattern) TypeConverters.convert("* test *", Pattern.class, null), false, null, null);
        assertNull(filter);
    } 
                            #location 4 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Test
    public void testThresholds() throws Exception {
        RegexFilter filter = RegexFilter.createFilter(".* test .*", null, false, null, null);
        filter.start();
        assertTrue(filter.isStarted());
        assertSame(Filter.Result.NEUTRAL,
                filter.filter(null, Level.DEBUG, null, "This is a test message", (Throwable) null));
        assertSame(Filter.Result.DENY, filter.filter(null, Level.ERROR, null, "This is not a test", (Throwable) null));
        LogEvent event = new Log4jLogEvent(null, null, null, Level.DEBUG, new SimpleMessage("Another test message"),
                null);
        assertSame(Filter.Result.NEUTRAL, filter.filter(event));
        event = new Log4jLogEvent(null, null, null, Level.ERROR, new SimpleMessage("test"), null);
        assertSame(Filter.Result.DENY, filter.filter(event));
        filter = RegexFilter.createFilter(null, null, false, null, null);
        assertNull(filter);
    }