def default_group_slice(self):
        """The default group slice of the view, or None if the view is not
        grouped.
        """
        if not self._has_slices:
            return None

        if self._dataset.default_group_slice not in self.group_slices:
            return self.group_slice

        return self._dataset.default_group_slice
The default group slice of the view, or None if the view is not
        grouped.
        
fiftyone/core/view.py