android - RetrofitError: Part body must not be null -

i having retrofit api call. , getting retrofit error of part body cannot null. please help. have checked domain. having 1 more 'get' working fine

java code

typedstring role = new typedstring("both");             int fbregisterflag = 0;             typedstring firstname = new typedstring("saurabh");             typedstring lastname = new typedstring("lahoti");             typedstring password = new typedstring("saurabh");             typedstring email = new typedstring("saurabh@clicklabs.edu");             typedstring mobile = new typedstring("9650076366");             typedstring college = new typedstring("dtu");             typedstring biodescription = new typedstring("dtu");             typedstring[] transcripts = {new typedstring("saurabh"), new typedstring("lahoti")};             int year = 2011;             typedstring[] majors = {new typedstring("saurabh"), new typedstring("lahoti")};             typedstring[] minors = {new typedstring("saurabh"), new typedstring("lahoti")};             int[] availability = {1, 2, 3};              webservices.register(role, firstname, lastname, fbregisterflag, password, new typedstring("gsdf"), new typedstring("sdfsdf"),                     college, year, email, new typedstring("sdfsdf"), mobile, majors, minors, biodescription, transcripts, 0, availability, majors, new callback<string>() {                          @override                         public void success(string s, response response) {                          }                          @override                         public void failure(retrofiterror error) {                          }                     }); 

retrofit interface

public interface webservices { @multipart @post("/api/user/signup") void register(@part("role") typedstring role,               @part("firstname") typedstring firstname,               @part("lastname") typedstring lastname,               @part("fbregisterflag") int fbflag,               @part("password") typedstring password,               @part("fbid") typedstring fbid,               @part("profilepicture")typedstring profile,               @part("college") typedstring college,               @part("year") int year,               @part("primaryemail") typedstring primaryemail,               @part("facebookemail") typedstring fbemail,               @part("mobilenumber") typedstring mobnumber,               @part("majors") typedstring [] majors,               @part("minors") typedstring [] minors,               @part("biodescription") typedstring bio,               @part("transcripts") typedstring [] transcripts,               @part("fee") int fee,               @part("availability") int [] availability,               @part("courses") typedstring [] courses,               callback <string> callback);              }