Attach files to a work item programmatically: null pointer

Hi,

I am trying to attach files to a work item programmatically. Here is the code

ItemProfile<IWorkItem> profile = IWorkItem.FULL_PROFILE;
IWorkItemWorkingCopyManager workingCopyManager = workItemClient.getWorkItemWorkingCopyManager();
workingCopyManager.connect(handle, profile, null);
WorkItemWorkingCopy workingCopy = workingCopyManager.getWorkingCopy(handle);
IWorkItemReferences references = workingCopy.getReferences();

URI uri = new URI("http", null, "jira-uat", -1, "/secure/attachment/10029/DupeFinder.java", null, null);
System.out.println(uri.toASCIIString());
IReference reference= IReferenceFactory.INSTANCE.createReferenceFromURI(uri, "DupeFinder.java");
if (reference != null) {
references.add(WorkItemEndPoints.ATTACHMENT, reference);
}
try{

workingCopyManager.save(new WorkItemWorkingCopy[]{workingCopy}, monitor);
}
catch (Exception e) {
e.printStackTrace();
}


Then I got the following exceptions (in the catch clause)

java.lang.NullPointerException
at com.ibm.team.workitem.client.internal.ArtifactLink.createUpdatedAttachment(ArtifactLink.java:269)
at com.ibm.team.workitem.client.internal.WorkItemWorkingCopyRegistry.saveWorkItems(WorkItemWorkingCopyRegistry.java:1745)
at com.ibm.team.workitem.client.internal.WorkItemWorkingCopyRegistry.saveAffected(WorkItemWorkingCopyRegistry.java:1667)
at com.ibm.team.workitem.client.internal.WorkItemWorkingCopyRegistry.save(WorkItemWorkingCopyRegistry.java:1568)
at com.ibm.team.workitem.client.internal.WorkItemWorkingCopyRegistry.save(WorkItemWorkingCopyRegistry.java:1539)
at com.ibm.team.workitem.client.internal.WorkItemWorkingCopyManager.save(WorkItemWorkingCopyManager.java:115)
at com.ibm.team.workitem.ide.ui.example.CreateWorkItemsInBg$1.runProtected(CreateWorkItemsInBg.java:186)
at com.ibm.team.foundation.client.util.FoundationJob.run(FoundationJob.java:68)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:55)

Within the Eclipse client instance, I would see a "unnamed" attachment. But save operation cannot be finished since the exception caught.

Any thing wrong with the code? Or how can I debug the source code? Thanks in advance.

Lin