[Building Sakai] NPE when createSubmission

[cn19998]

Hello everyone,
 
I tired to create new submission to an assignment using SOAP  "Assignments.jws". However, every time I got NullPointerException from  the server.
 
The method in Assignments.jws is as follows:
 public String createSubmission(String sessionId, String context, String assignmentId, String userId, long time)  
I have identified different Excptions throw by illegal arguments,  like IdUnusedException for wrong sessionId and etc. I am sure that all  arguments are correct (except String context, I think it to be the  content of my submission since it's the only param where I can pass the  content of submission) . But it still thorws NullPointerException from  the server. Here's the log:
 2014-05-24 11:12:16,573  INFO http-bio-8080-exec-10 org.sakaiproject.util.RemoteHostFilter - Access granted (.*): 127.0.0.1/127.0.0.1 2014-05-24 11:12:16,635  INFO http-bio-8080-exec-8 org.sakaiproject.util.RemoteHostFilter - Access granted (.*): 127.0.0.1/127.0.0.1 2014-05-24 11:12:16,641  WARN http-bio-8080-exec-8 org.sakaiproject.assignment.impl.BaseAssignmentService - org.sakaiproject.assignment.impl.DbAssignmentService at 5b33a4b0 ADD SUBMISSION: cannot add submission object with submission id=70976923-797c-431c-a7af-4e0a80b82849, assignment id=142c8ef4-2c0d-4119-9890-c08a5c2fedff, and submitter id=admin 2014-05-24 11:12:16,642 ERROR http-bio-8080-exec-8 Assignments - WS createSubmission(): java.lang.NullPointerException : null 2014-05-24 11:12:16,652  INFO http-bio-8080-exec-10 org.sakaiproject.util.RemoteHostFilter - Access granted (.*): 127.0.0.1/127.0.0.1  
In the Assignments.jws, I identified (using LOG.error("message") to set breakpoints) that the error come since this few lines :


    AssignmentSubmissionEdit ase = assignmentService.addSubmission(context,assignmentId, userDirectoryService.getUserId(userId));     ase.clearSubmitters();   // Here's throws NullPointerException     ase.addSubmitter(user);     ase.setSubmitted(true);     Time subTime = timeService.newTime(time);     LOG.info("Setting time to " + time);     ase.setTimeSubmitted(subTime);     assignmentService.commitEdit(ase);     return ase.getId();
 
As a green hand, I don't understand how things are going on here. I  am trying to develop a local client for Sakai. Could someone suggests  something? Am I misunderstanding something here?
 
BTW, are there any EntityProvider for posting a submission? There's  assignment entity, but I can not find anyone for submissions.
 
Thanks.
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