rx.zip and rx.combineLast are not work anymore

[luohao123]

i have a code previous without nullsafety, but after nullsafety, not work any more

Stream<String> createTask(int? exitsTaskId) {
    debugPrint("createTask called?? ");
    var res = Rx.combineLatest6(
        selectedProject,
        dueDateSelected,
        dueTimeSelected,
        prioritySelected,
        comment,
        repeatedOptionSelected, (Project project,
            int dueDateSelected,
            int dueTimeSelected,
            Status status,
            String comment,
            RepeatedOption repeatedOption) {
      List<int> labelIds = [];

the code inside rx can not be trigger. why