#vulnerable code 
                                @Test
    public void testResign() throws Exception {
        copyToTestPath(originalFolder, Collections.singletonList(singedApks.get(0)));
        File signedApk = originalFolder.listFiles()[0];

        String cmd = "-" + CLIParser.ARG_APK_FILE + " " + signedApk.getAbsolutePath() + " -" + CLIParser.ARG_APK_OUT + " " + outFolder.getAbsolutePath() + " --skipZipAlign --allowResign --debug --ks " + testReleaseKs.getAbsolutePath() + " --ksPass " + ksPass + " --ksKeyPass " + keyPass + " --ksAlias " + ksAlias;

        System.out.println(cmd);
        SignTool.Result result = SignTool.mainExecute(CLIParserTest.asArgArray(cmd));
        assertNotNull(result);
        assertEquals(0, result.unsuccessful);
        assertEquals(1, result.success);
        assertEquals(1, outFolder.listFiles().length);
        AndroidApkSignerVerify.Result verifyResult = new AndroidApkSignerVerify().verify(outFolder.listFiles()[0], null, null, false);
        assertTrue(verifyResult.verified);
        assertEquals(0, verifyResult.warnings.size());
        assertEquals(0, verifyResult.errors.size());
        assertEquals(releaseCertSha256, verifyResult.certInfoList.get(0).certSha256);
    } 
                            #location 4 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Test
    public void testResign() throws Exception {
        List<File> signedApks = copyToTestPath(originalFolder, Collections.singletonList(singedApks.get(0)));
        File signedApk = signedApks.get(0);

        String cmd = "-" + CLIParser.ARG_APK_FILE + " " + signedApk.getAbsolutePath() + " -" + CLIParser.ARG_APK_OUT + " " + outFolder.getAbsolutePath() + " --skipZipAlign --allowResign --debug --ks " + testReleaseKs.getAbsolutePath() + " --ksPass " + ksPass + " --ksKeyPass " + keyPass + " --ksAlias " + ksAlias;

        System.out.println(cmd);
        SignTool.Result result = SignTool.mainExecute(CLIParserTest.asArgArray(cmd));
        assertNotNull(result);
        assertEquals(0, result.unsuccessful);
        assertEquals(1, result.success);
        assertEquals(1, outFolder.listFiles().length);
        AndroidApkSignerVerify.Result verifyResult = new AndroidApkSignerVerify().verify(outFolder.listFiles()[0], null, null, false);
        assertTrue(verifyResult.verified);
        assertEquals(0, verifyResult.warnings.size());
        assertEquals(0, verifyResult.errors.size());
        assertEquals(releaseCertSha256, verifyResult.certInfoList.get(0).certSha256);
    }