#vulnerable code 
                                @Test
    public void testMemMapExtendsIfNeeded() throws Exception {
        final File f = new File(LOGFILE);
        if (f.exists()) {
            assertTrue(f.delete());
        }
        assertTrue(!f.exists());

        final Logger log = LogManager.getLogger();
        final char[] text = new char[200];
        Arrays.fill(text, 'A');
        try {
            log.warn("Test log1");
            assertTrue(f.exists());
            assertEquals("initial length", 256, f.length());

            log.warn(new String(text));
            assertEquals("grown", 256 * 2, f.length());
            
            log.warn(new String(text));
            assertEquals("grown again", 256 * 3, f.length());
        } finally {
            CoreLoggerContexts.stopLoggerContext(false);
        }
        final int LINESEP = System.getProperty("line.separator").length();
        assertEquals("Shrunk to actual used size", 658 + 3 * LINESEP, f.length());

        String line1, line2, line3, line4;
        try (final BufferedReader reader = new BufferedReader(new FileReader(LOGFILE))) {
            line1 = reader.readLine();
            line2 = reader.readLine();
            line3 = reader.readLine();
            line4 = reader.readLine();
        }
        assertNotNull(line1);
        assertThat(line1, containsString("Test log1"));

        assertNotNull(line2);
        assertThat(line2, containsString(new String(text)));

        assertNotNull(line3);
        assertThat(line3, containsString(new String(text)));

        assertNull("only three lines were logged", line4);
    } 
                            #location 25 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Test
    public void testMemMapExtendsIfNeeded() throws Exception {
        final File f = new File(LOGFILE);
        if (f.exists()) {
            assertTrue(f.delete());
        }
        assertTrue(!f.exists());

        final Logger log = LogManager.getLogger();
        final char[] text = new char[200];
        Arrays.fill(text, 'A');
        try {
            log.warn("Test log1");
            assertTrue(f.exists());
            assertEquals("initial length", 256, f.length());

            log.warn(new String(text));
            assertEquals("grown", 256 * 2, f.length());
            
            log.warn(new String(text));
            assertEquals("grown again", 256 * 3, f.length());
        } finally {
            CoreLoggerContexts.stopLoggerContext(false);
        }
        final int LINESEP = System.lineSeparator().length();
        assertEquals("Shrunk to actual used size", 658 + 3 * LINESEP, f.length());

        String line1, line2, line3, line4;
        try (final BufferedReader reader = new BufferedReader(new FileReader(LOGFILE))) {
            line1 = reader.readLine();
            line2 = reader.readLine();
            line3 = reader.readLine();
            line4 = reader.readLine();
        }
        assertNotNull(line1);
        assertThat(line1, containsString("Test log1"));

        assertNotNull(line2);
        assertThat(line2, containsString(new String(text)));

        assertNotNull(line3);
        assertThat(line3, containsString(new String(text)));

        assertNull("only three lines were logged", line4);
    }