def close(self):
        """ close: Close zipfile when done
            Args: None
            Returns: None
        """
        index_present = self.contains('index.html')
        self.zf.close() # Make sure zipfile closes no matter what
        if not index_present:
            raise ReferenceError("Invalid Zip at {}: missing index.html file (use write_index_contents method)".format(self.write_to_path))
close: Close zipfile when done
            Args: None
            Returns: None