Problem in AttributeRole

@Override
		public void doWork() throws OperatorException 
		{
			File file = getParameterAsFile("example_set_file");
			ExampleSet eSet = exampleSetInput.getData();
			try 
			{	
				Attribute sum = AttributeFactory.createAttribute("sum", Attributes.SPECIAL);

				eSet.getExampleTable().addAttribute(sum);
				eSet.getAttributes().add(eSet.getAttributes().findRoleByName("id"));
			}
			catch (IOException e) 
			{
				throw new UserError(this, 303, file, e.getMessage());
			}
			exampleSetOutput.deliver(eSet);
		}

What is worng in the code??