我想这一定是一个get请求hostname/match？data=“yffyf”

@GET("match")
    Call<ResponseBody> add_user(
            @Query("data") String data);

但是出现了一个错误

public void sendPost(String gk ) throws IOException {
        Call<ResponseBody> call = ApiUtils.getAPIService().add_user(scanResults.getText().toString());
        call.enqueue(new Callback<ResponseBody>() {
            @Override
            public void onResponse(Call<ResponseBody> call, Response<ResponseBody> response) {
                try {
                    String s = response.body().string();
                    Toast.makeText(MainActivity.this, s, Toast.LENGTH_SHORT).show();

                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

            @Override
            public void onFailure(Call<ResponseBody> call, Throwable t) {

                Toast.makeText(MainActivity.this, t.getMessage().toString(), Toast.LENGTH_SHORT).show();
            }
        });
    }

ava.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String okhttp3.ResponseBody.string()' on a null object reference
    at com.uthoo.www.ocr.MainActivity$3.onResponse(MainActivity.java:95)
    at retrofit2.ExecutorCallAdapterFactory$ExecutorCallbackCall$1$1.run(ExecutorCallAdapterFactory.java:70)
    at android.os.Handler.handleCallback(Handler.java:873)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:201)
    at android.app.ActivityThread.main(ActivityThread.java:6831)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:547)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:927)

你能告诉我如何使用post和get来实现这一点吗？谢谢您。。。