MockService won't return response when request is made from Java app

I've written some code to do a POST request with octet-stream content type and an attachment,

When I call my mock service from SoapUI call or Postman a response is returned. But when I call via Java code I can see the requests get to mock service, I can print the content and headers but the response is not returning.

There's an error: 

• 2018-02-27 08:55:36.920: [dispatch error; missing response]

The headers of POST are the same in Postman as in Java, I made sure of that so I don't know what is the issue here.