title: Value missing though required retrofit 2.0
body: <p>I am using Retrofit 2.0 to create retrofit service for uploading file on server.</p>
  
  <p>I am refering <a href="https://futurestud.io/blog/retrofit-2-how-to-upload-files-to-server" rel="nofollow noreferrer">https://futurestud.io/blog/retrofit-2-how-to-upload-files-to-server</a></p>
  
  <p>Below is my FileUploadService code:</p>
  
  <pre><code>interface TripHistoryFileUploadService {
  @Multipart
  @POST("trip/trip-history")
  Call&lt;ResponseBody&gt; upload(@Part("json_file") RequestBody description,
                            @Part MultipartBody.Part file);
  </code></pre>
  
  <p>}</p>
  
  <p>I am using below retrofit version:</p>
  
  <pre><code> compile 'com.squareup.retrofit2:retrofit:2.0.0-beta4'
  </code></pre>
  
  <p>But I am getting error <strong>Value missing though required</strong> like below:</p>
  
  <p><a href="https://i.stack.imgur.com/s3IB5.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/s3IB5.png" alt="enter image description here"></a></p>
  
  <p>Can any one face same problem or any one have solution for the same?</p>