Convert a VEX block to an AIL block.

        :param block_node:  A BlockNode instance.
        :return:            An converted AIL block.
        :rtype:             ailment.Block

def _convert(self, block_node):
        """
        Convert a VEX block to an AIL block.

        :param block_node:  A BlockNode instance.
        :return:            An converted AIL block.
        :rtype:             ailment.Block
        """

        if not type(block_node) is BlockNode:
            return block_node

        block = self.project.factory.block(block_node.addr, block_node.size)

        ail_block = ailment.IRSBConverter.convert(block.vex, self._ail_manager)
        return ail_block