title: Return null in response
body: <p>This is my code, I don't know what's wrong with it. It is just a simple login.</p>
  
  <p>Main Activity </p>
  
  <pre><code>public class MainActivity extends AppCompatActivity {
  
      private login login;
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
  
          Retrofit retrofit = new Retrofit.Builder()
                  .baseUrl("http://services.hanselandpetal.com/")
                  .addConverterFactory(GsonConverterFactory.create())
                  .build();
          login = retrofit.create(login.class);
  
          Button btnLogin = findViewById(R.id.btn_log_out);
  
          btnLogin.setOnClickListener(new View.OnClickListener() {
              @Override
              public void onClick(View v) {
  
                  login.isLogin("eslam@yahoo.com","123").enqueue(new Callback&lt;ResponseBody&gt;() {
                      @Override
                      public void onResponse(Call&lt;ResponseBody&gt; call, Response&lt;ResponseBody&gt; response) {
                          try {
                              assert response.body() != null;
                              String MyResult = response.body().string();
                              Log.d("sample",MyResult);
                          }catch (IOException e){
                              e.printStackTrace();
                          }
                      }
  
                      @Override
                      public void onFailure(Call&lt;ResponseBody&gt; call, Throwable t) {
  
                      }
                  });
              }
          });
  
      }
  
  }
  </code></pre>
  
  <p>Interface </p>
  
  <pre><code>public interface login {
  
      @GET("api/register")
      Call&lt;ResponseBody&gt; isLogin(@Query("Email") String Email,@Query("Password") String Password);
  
  }
  </code></pre>