改造返回null

Question

我正尝试将请求进行翻新。但改型返回null并运行Failure方法。

问题不是主机。我在邮递员上尝试了该请求，但没有问题。

public class LoginActivity extends AppCompatActivity{

EditText searchEdit;
Button btn;

@Override
protected void onCreate(@Nullable Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_login);

    searchEdit = (EditText) findViewById(R.id.searchEditXml);

    btn.setOnClickListener(new View.OnClickListener()
    {
        @Override
        public void onClick(View view)
        {
            FakeTwitterProvider twitterProvider = new FakeTwitterProvider();

            MyApi myApi = twitterProvider.getTService();

            Fields fields = new Fields();

            fields.search = searchEdit.getText().toString();

            Call<Fields> call = myApi.createTweet(fields);
            call.enqueue(new Callback<Fields>()
            {
                @Override
                public void onResponse(Call<Fields> call, retrofit2.Response<Fields> response)
                {
                    if (response.isSuccessful())
                    {
                        Log.e("1", String.valueOf(response.body()));
                        Toast.makeText(getBaseContext(), "successfull" + response.body(), Toast.LENGTH_SHORT).show();
                        //String a = response.body().toString();
                    }
                    else
                    {
                        Log.e("0", String.valueOf(response.body()));
                        Toast.makeText(getBaseContext(), "http request fail" + response.code(), Toast.LENGTH_SHORT).show();
                    }
                }

                @Override
                public void onFailure(Call<Fields> call, Throwable t)
                {
                    Log.e("1","00000000000000000000");
                    Toast.makeText(getBaseContext(), "fail it" + t.getCause(), Toast.LENGTH_LONG).show();
                }
            });


        }
    });}

这是我的改造界面：

public interface MyApi
{
    @POST("/news_folder/search.php/")
    Call<Fields> createTweet(@Body Fields fields);
}

url变量的url类：

public class Urlclass
{
    public static final String url = "http://mywebsite.com/";
}

改装类：

public class FakeTwitterProvider
{
private MyApi mTService;

public FakeTwitterProvider()
{
    OkHttpClient httpClient = new OkHttpClient();

    Retrofit retrofit = new Retrofit.Builder()
            .baseUrl(Urlclass.url)
            .client(httpClient)
            .addConverterFactory(GsonConverterFactory.create())
            .build();

    mTService = retrofit.create(MyApi.class);
}

public MyApi getTService()
{
    return mTService;
}
}

和我的领域：

public class Fields
{
    @SerializedName("search")
    public String search;
}

哪一部分错了？