def insert_instance(self, block):
        """Insert a fetched instance into embed block."""

        embed_type = block.get('type', None)
        data = block.get('data', {})
        serializer = self.serializers.get(embed_type, None)

        if serializer is None:
            return block

        try:
            instance_id = serializer.get_id(data)
            instance = self.instances[embed_type][instance_id]
            data[embed_type] = serializer.serialize(instance)
        except:
            data[embed_type] = None

        block['data'] = data

        return block
Insert a fetched instance into embed block.