def get_mask_targets(self, field):
        """Gets the mask targets for the given field, or None if no mask
        targets are available.

        Mask targets are first retrieved from :meth:`mask_targets` if they
        exist, otherwise from :meth:`default_mask_targets`.

        Args:
            field: a field name

        Returns:
            a list of classes, or None
        """
        if field in self.mask_targets:
            return self.mask_targets[field]

        if self.default_mask_targets:
            return self.default_mask_targets

        return None
Gets the mask targets for the given field, or None if no mask
        targets are available.

        Mask targets are first retrieved from :meth:`mask_targets` if they
        exist, otherwise from :meth:`default_mask_targets`.

        Args:
            field: a field name

        Returns:
            a list of classes, or None
        
fiftyone/core/collections.py