Retrofit2 error java.io.EOFException: End of input at line 1 column 1

Question

I called PATCH web service using Retrofit2 but onResponse is not called and the onFailure is called Despite of the operation of the service is succeeded on the server side perfectly

And whenever,I tried to use fiddler to check the service its working , i found the problem is that serializing the coming response of the service and when using fiddler i found that no content of the JSON response so the Retrofit service assumed that its failed because there is no content and it cannot serialize the EMPTY content and give me this error

java.io.EOFException: End of input at line 1 column 1

Fiddler raw Response

HTTP/1.1 200 OK
Server: nginx/1.9.4
Date: Wed, 02 Mar 2016 09:55:55 GMT
Content-Type: application/json
Content-Length: 0
Connection: close
Status: 200 OK
X-Content-Type-Options: nosniff

Fiddler Json Response is empty

webservice in java

Call<Object> call = TimeCapp.services.accept_invited_alerts(HomeActivity.api_token, alert_id);

call.enqueue(new Callback<Object>()
{
    @Override
    public void onResponse (Call<Object> call, Response<Object> response)
    {
        if (response.isSuccess()) {
            String x = response.body();
        }
    }
    @Override
    public void onFailure (Call<Object>call, Throwable t)
    {
        String x = t.getMessage();//java.io.EOFException: End of input at line 1 column 1
    }
}

I tried to replace object with String,JsonObject,emptyCalssBody .... but its failed

the interface of the webservice

@PATCH("alerts/{alert_id}/accept")
Call<Object> accept_invited_alerts(@Header("X-Api-Token") String  
api_token, @Path("alert_id") int alert_id);

Answer 1

just return void instead, if the body is empty

@PATCH("alerts/{alert_id}/accept") Call<Void> accept_invited_alerts(@Header("X-Api-Token") String api_token, @Path("alert_id") int alert_id);

for retrofit with Rx java you can use something like this

@PATCH("alerts/{alert_id}/accept") Observable<Response<Void>> accept_invited_alerts(@Header("X-Api-Token") String api_token, @Path("alert_id") int alert_id);

EDIT: For kotlin

@PATCH("alerts/{alert_id}/accept")
fun accept_invited_alerts(@Header("X-Api-Token")  api_token: String, @Path("alert_id") alert_id: Int): Call<Unit>

and

@PATCH("alerts/{alert_id}/accept")
fun accept_invited_alerts(@Header("X-Api-Token") api_token: String, @Path("alert_id") alert_id: Int): Observable<Response<Unit>>