DataBunch for MaskRCNN type dataset

Hi, I am trying to implement MaskRCNN using fastai framework. I need to create a ItemList with Item that can hold segment, bbox and key_points. How do I go about it?

So far I have thought of implementing this in lines of below snippet of code. Appreciate your comments.
Thanks in advance.

class ImageSegmentsAndKeyPoints(ImageBBox):
     bbox: FlowField
     point: FlowField
     segment: Image

    def show():

class MaskCategoryList(ObjectCategoryList, SegmentationCategoryList):

    def get(self, i):
        return ImageSegmentsAndKeyPoints.create(
            *_get_size(self.x, i),


class MaskItemList(MaskCategoryList):