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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 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: '<html><head></head><body>Hi!</body></html>' """

        if encoding:
            return b"".join(list(self.serialize(treewalker, encoding)))
        else:
            return "".join(list(self.serialize(treewalker)))