#vulnerable code 
                                @Test
    public void testServer() throws IOException {
        String serverUrl = String.format("http://localhost:%s/%s", serverPort,
                path);
        OkHttpClient client = new OkHttpClient();
        Request request = new Request.Builder().url(serverUrl).build();
        Response response = client.newCall(request).execute();

        assertTrue(response.isSuccessful());

        ResponseBody body = response.body();
        log.debug("Content-Type {}", body.contentType());
        log.debug("Content-Length {}", body.contentLength());
    } 
                            #location 12 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Test
    public void testServer() throws IOException {
        String serverUrl = String.format("http://localhost:%s/%s", serverPort,
                path);
        OkHttpClient client = new OkHttpClient();
        Request request = new Request.Builder().url(serverUrl).build();

        // Assert response
        Response response = client.newCall(request).execute();
        assertTrue(response.isSuccessful());

        // Assert attachment
        String attachment = String.format("attachment; filename=\"%s\"",
                driver);
        assertTrue(response.headers().values("Content-Disposition")
                .contains(attachment));
    }