code: def render(self, treewalker, encoding=None):
          
          if encoding:
              return b"".join(list(self.serialize(treewalker, encoding)))
          else:
              return "".join(list(self.serialize(treewalker)))
docs: 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>'