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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 get_payee_channel( channelidentifiers_to_channels: ChannelMap, transfer_pair: MediationPairState, ) -> Optional[NettingChannelState]: """ Returns the payee channel of a given transfer pair or None if it's not found """

    payee_channel_identifier = transfer_pair.payee_transfer.balance_proof.channel_identifier
    return channelidentifiers_to_channels.get(payee_channel_identifier)