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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 do_build(self):
 """ Create the default version of the layer :return: a string of the packet with the payload """

        if not self.explicit:
            self = next(iter(self))
        pkt = self.self_build()
        for t in self.post_transforms:
            pkt = t(pkt)
        pay = self.do_build_payload()
        if self.raw_packet_cache is None:
            return self.post_build(pkt, pay)
        else:
            return pkt + pay