Problem to set header with jersey for rest client

See more:

Java

REST

client-server

I tried to upload a document to a document server with Jersey. But curiously I can't set a header value. If I set the value as query param(server supports it) all works fine. But I wan't set it in the header. Here is my Java Code:

Client client =ClientBuilder.newClient()
                    .register(JacksonFeature.class)
                    .register(MultiPartFeature.class);
            WebTarget webTarget=client.target("http://.../documents").queryParam("Token",token);//works
            FileDataBodyPart fileDataBodyPart = new FileDataBodyPart("filedata", file, MediaType.APPLICATION_OCTET_STREAM_TYPE);
            MultiPart multiPart = new MultiPart();
            multiPart.setMediaType(MediaType.MULTIPART_FORM_DATA_TYPE);
            multiPart.bodyPart(fileDataBodyPart);
            Response response=webTarget.request(MediaType.APPLICATION_JSON_TYPE)
.header("Token",token)//header don't works
                    .post(Entity.entity(multiPart,multiPart.getMediaType()));

I tried the same in Ruby and it works for the same URL with the same values and the Token param in the header:

require 'rest-client'
...
resp=RestClient.post url, JSON.generate(conversion_options), {content_type: :json,
                                                              accept: :json,
                                                              Token: token}
#Third param is header values
...

Is there a bug in Jersey for setting headers? My version is 2.22.2.

Thanks for helpful comments.

What I have tried:

Tried it with Ruby, in upper and lower and diverse possible solutions with Jersey.