code: @Override
  	public Response joinMember(JoinForm joinInfo) throws PopbillException {
  		String postData = toJsonString(joinInfo);
  
  		return httppost("/Join", null, postData, null, Response.class);
  	}
docs: /* (non-Javadoc)
  @see com.popbill.api.BaseService#joinMember(com.popbill.api.JoinForm)