Adding child not working using Java Api

	private static class LinkWorkItemOperation extends WorkItemOperation {

		private IWorkItemHandle fOpposite;
		private IEndPointDescriptor fEndpointDescriptor;

		public LinkWorkItemOperation(IEndPointDescriptor endpointDescriptor,
				IWorkItemHandle opposite) {
			super("Linking Work Item", IWorkItem.FULL_PROFILE);
			fOpposite = opposite;
			fEndpointDescriptor = endpointDescriptor;
		}

		@Override
		protected void execute(WorkItemWorkingCopy workingCopy,
				IProgressMonitor monitor) throws TeamRepositoryException {
			IItemReference reference = IReferenceFactory.INSTANCE
					.createReferenceToItem(fOpposite);
			workingCopy.getReferences().add(fEndpointDescriptor, reference);
		}
	}

		LinkParentWorkItemOperation operationParent = new LinkWorkItemOperation(
				ILinkTypeRegistry.INSTANCE.getLinkType(
						WorkItemLinkTypes.PARENT_WORK_ITEM)
						.getSourceEndPointDescriptor(), linkdest);
		operationback.run(opposite, monitor);