def cast_to_swimlane(self, value):
value = super(ListField, self).cast_to_swimlane(value)<EOL>if not value:<EOL><INDENT>return None<EOL><DEDENT>value_ids = deepcopy(self._initial_value_to_ids_map)<EOL>return [self._build_list_item(item, value_ids[item].pop(<NUM_LIT:0>) if value_ids[item] else None) for item in value]<EOL>
Restore swimlane format, attempting to keep initial IDs for any previously existing values