Bug 105697 [Undo] - OperationHistoryEvent - cannot distinguish between canceled event or failed event
bundles/org.eclipse.core.commands/src/org/eclipse/core/commands/operations/DefaultOperationHistory.java
return null;
	}
	/*
	 * Consult the IOperationApprovers to see if the proposed undo should be
	 * allowed.
	 */
	private IStatus getUndoApproval(IUndoableOperation operation,
			IAdaptable info) {
		
		
		
		final IOperationApprover[] approverArray = (IOperationApprover[]) approvers
				.toArray(new IOperationApprover[approvers.size()]);
		for (int i = 0; i < approverArray.length; i++) {
			IOperationApprover approver = approverArray[i];
			IStatus approval = approver.proceedUndoing(operation, this, info);
			if (!approval.isOK()) {
				if (DEBUG_OPERATION_HISTORY_APPROVAL) {
					System.out
							.print("OPERATIONHISTORY >>> Undo not approved by ");  
					System.out.print(approver);
					System.out.print("for operation ");  
					System.out.print(operation);
					System.out.print(" with status ");  
					System.out.print(approval);
					System.out.println();
				}
				return approval;
			}
		}