json - How to add a parameter to RxClient web request? -

i've following working code make async http call using rxclient(see import). however, when there json content, receive following error , couldn't figure out how can pass json parameter in case. fyi: json call post rest of code makes call. calls work w/o json content.

http error 411. request must chunked or have content length.</p>

import com.google.inject.inject;  import org.glassfish.jersey.client.rx.rxclient; import org.glassfish.jersey.client.rx.rxinvocationbuilder; import org.glassfish.jersey.client.rx.rxwebtarget; import org.glassfish.jersey.client.rx.rxjava.rxobservableinvoker;  import java.io.unsupportedencodingexception; import java.net.urlencoder;  import javax.ws.rs.core.response;  import rx.observable; import rx.functions.func1; import rx.schedulers.schedulers; public class emprxclient {    private rxclient<rxobservableinvoker> httpclient;    @inject   public emprxclient(rxclient<rxobservableinvoker> httpclient) {     this.httpclient = httpclient;   }    public <t> observable<t> fetchresult(string url, string token, string jsoncontent, string method, func1<response, t> mapper) {      rxwebtarget<rxobservableinvoker> rxwebtarget = httpclient.target(url);      rxinvocationbuilder<rxobservableinvoker> rxinvocationbuilder;      if (jsoncontent != null&& rxwebtarget!=null)       rxinvocationbuilder = rxwebtarget.request(jsoncontent);     else       rxinvocationbuilder = rxwebtarget.request();      return rxinvocationbuilder         .header("authorization", "bearer " + token)         .header("content-type", "application/json")         .header("accept", "application/json")         .header("grant_type", "client_credentials")         .rx()         .method(method)         .subscribeon(schedulers.io())         .map(mapper);   } }