public Optional<OPFItem> getItemById(String id)
  {
    return Optional.fromNullable(itemsById.get(id));
  }
public Optional < OPFItem > getItemById ( String id ) { return Optional . fromNullable ( itemsById . get ( id ) ) ; }
Search the item with the given ID.

@param id
the ID of the item to search, can be <code>null</code>.
@return An {@link Optional} containing the item if found, or
{@link Optional#absent()} if not found.