code: public Operation getOperation(String id) {
          for (Iterator<Operation> it = operations.iterator(); it.hasNext();) {
              Operation oper = it.next();
              if (oper.getId().compareTo(id) == 0) {
                  return oper;
              }
          }
          return null;
      }
docs: Returns the operation of the given id or a new default operation. If no
  operation was found, null is returned.
  
  @param id The id
  @return The operation