private void doModify(Task _task, Task t, boolean unredo,
			LocalDateTime newStartTime, LocalDateTime newEndTime,
			String newCategory, String newPriority, TaskData taskToModify,
			LocalDateTime oldStartTime, LocalDateTime oldEndTime,
			String oldCategory, String oldPriority) {
		if (newStartTime != null || unredo) {
			taskToModify.setStartDateTime(newStartTime);
			t.setStartDateTime(newStartTime);
			_task.setStartDateTime(oldStartTime);
		} else {
			t.setStartDateTime(oldStartTime);
			_task.setStartDateTime(oldStartTime);
		}
		if (newEndTime != null || unredo) {
			taskToModify.setEndDateTime(newEndTime);
			t.setEndDateTime(newEndTime);
			_task.setEndDateTime(oldEndTime);
		} else {
			t.setEndDateTime(oldEndTime);
			_task.setEndDateTime(oldEndTime);
		}
		if (newCategory != null || unredo) {
			taskToModify.setCategory(newCategory);
			t.setCategory(newCategory);
			_task.setCategory(oldCategory);
		} else {
			t.setCategory(oldCategory);
			_task.setCategory(oldCategory);
		}
		if (newPriority != null || unredo) {
			taskToModify.setPriority(newPriority);
			t.setPriority(newPriority);
			_task.setPriority(oldPriority);
		} else {
			t.setPriority(oldPriority);
			_task.setPriority(oldPriority);
		}
	}