How to stop loop actions??? and Custom function problem

I have a created custom function in which i want create task automatically and its working the only problem i am facing is that i am not able store the value which is generated from the output in the database Supbase.
In the image you can see that i am generating duedate but when i run the function in database the due date colm is NULL and rest all values are entering ,how to add that duedate value in my database Supabase?????
Can anyone help me this problem????

String? automatictasktestingfucntion(
  String? enddate,
  String? taskname,
  String? description,
  String? duedate,
) {
  /// MODIFY CODE ONLY BELOW THIS LINE

  // Check if any of the required arguments are missing
  if (enddate == null || taskname == null || description == null) {
    return null;
  }

  // Parse the end date
  final formatter = DateFormat('yyyy-MM-dd');
  final endDate = formatter.parse(enddate);

  // Get the current date
  final currentDate = DateTime.now();

  // Create a list to store task messages
  final List<String> taskMessages = [];

  // Iterate from the current date until the end date, creating tasks for each Tuesday
  for (DateTime date = currentDate;
      date.isBefore(endDate.add(Duration(days: 1))); // Include end date
      date = date.add(Duration(days: 1))) {
    if (date.weekday == DateTime.tuesday) {
      // Create due date based on the current date
      final dueDate =
          date.subtract(Duration(days: date.weekday - DateTime.tuesday));

      // Create a task message with the provided details, end date, and due date
      final taskMessage =
          'Task: $taskname\nDescription: $description\nEnd Date: ${formatter.format(endDate)}\nDue Date: ${formatter.format(dueDate)}';

      taskMessages.add(taskMessage);
    }
  }

  // Combine task messages into a single string separated by newlines
  final combinedTaskMessages = taskMessages.join('\n');

  return combinedTaskMessages;

  /// MODIFY CODE ONLY ABOVE THIS LINE
}