def render(self, treewalker, encoding=None):
        """Serializes the stream from the treewalker into a string

        :arg treewalker: the treewalker to serialize

        :arg encoding: the string encoding to use

        :returns: the serialized tree

        Example:

        >>> from html5lib import parse, getTreeWalker
        >>> from html5lib.serializer import HTMLSerializer
        >>> token_stream = parse('<html><body>Hi!</body></html>')
        >>> walker = getTreeWalker('etree')
        >>> serializer = HTMLSerializer(omit_optional_tags=False)
        >>> serializer.render(walker(token_stream))
        '<html><head></head><body>Hi!</body></html>'

        """
        if encoding:
            return b"".join(list(self.serialize(treewalker, encoding)))
        else:
            return "".join(list(self.serialize(treewalker)))
Serializes the stream from the treewalker into a string

        :arg treewalker: the treewalker to serialize

        :arg encoding: the string encoding to use

        :returns: the serialized tree

        Example:

        >>> from html5lib import parse, getTreeWalker
        >>> from html5lib.serializer import HTMLSerializer
        >>> token_stream = parse('<html><body>Hi!</body></html>')
        >>> walker = getTreeWalker('etree')
        >>> serializer = HTMLSerializer(omit_optional_tags=False)
        >>> serializer.render(walker(token_stream))
        '<html><head></head><body>Hi!</body></html>'