Multi-task Text Classification in fastai

Hi all. I want to build a text classifier for multi-task using fastai.
The classifier consists of 2 tasks:

multitask_project = {
    'A': {
        'label_lists': ic_labels,
        'metric': accuracy
    'B': {
        'label_lists': sic_labels,
        'metric': accuracy

I built class class MultitaskLabelLists(LabelLists) to custom label instead of LabelLists in fastai and when call to databunch, the following error occurred:

Help me, thanks all.