Deliver by using plainJava API

The code as follow, I've check in, but an exception throw when program call the last line code:

com.ibm.team.scm.common.ChangeSetsNotOutgoingException: These change sets are not outgoing and therefore cannot be delivered.
 at com.ibm.team.scm.client.internal.WorkspaceConnection.checkAgainstReport(WorkspaceConnection.java:2120)
 at com.ibm.team.scm.client.internal.WorkspaceConnection.runDeliver(WorkspaceConnection.java:2012)

My Code:

IChangeSet changeSetToDeliver = null;
   List<IChangeSetHandle> activeChangeSets = workspaceConnection.activeChangeSets(comp);
   System.out.println("Active ChangeSets: " + activeChangeSets.size());
   for (IChangeSetHandle changeSetHandle : activeChangeSets) {
    if (changeSetHandle instanceof IChangeSet) {

     changeSetToDeliver = (IChangeSet) changeSetHandle;
    }
   }
   
   IChangeSetHandle ics = workspaceConnection.getCurrentChangeSet(comp);
   System.out.println("IChangeSetHandle:" + ics);//Here output is 0
   
   
   // deliver the code
   IChangeHistorySyncReport sync = workspaceConnection.compareTo(workspaceConnection, WorkspaceComparisonFlags.CHANGE_SET_COMPARISON_ONLY, Collections.EMPTY_LIST, null);//The 3rd parameter could be used to exclude components on the workspace from the compare operation
   List list = sync.outgoingChangeSets(comp);
   System.out.println("Out going change sets size:" + list.size()); //Here output is 0
   workspaceConnection.deliver(workspaceConnection, sync, workspaceConnection.getBaselineSets(null), Arrays.asList(new IChangeSet[]{changeSetToDeliver}), null);

Is there any one can help for this issue? how should I make the change set to out going chengeset ?

And I know the last line code should be:

workspaceConnection.deliver(workspaceConnection, sync, workspaceConnection.getBaselineSets(null), sync.outgoingChangeSets(comp), null);

But as you can see the out going size is 0 ,but the change set above I get it, which is not 0.