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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 _lease_valid(self, lease):
 """ Check if the given lease exist and still has a prefix that owns it. If the lease exist but its prefix isn't, remove the lease from this store. Args: lease (lago.subnet_lease.Lease):
 Object representation of the lease Returns: str or None: If the lease and its prefix exists, return the path to the uuid of the prefix, else return None. """

        if not lease.exist:
            return None

        if lease.has_env:
            return lease.uuid_path
        else:
            self._release(lease)
            return None