Return the token network address for the given token or None if
        there is no correspoding address.

def get_token_network(
            self,
            token_address: TokenAddress,
            block_identifier: BlockSpecification = 'latest',
    ) -> Optional[Address]:
        """ Return the token network address for the given token or None if
        there is no correspoding address.
        """
        if not isinstance(token_address, T_TargetAddress):
            raise ValueError('token_address must be an address')

        address = self.proxy.contract.functions.token_to_token_networks(
            to_checksum_address(token_address),
        ).call(block_identifier=block_identifier)
        address = to_canonical_address(address)

        if is_same_address(address, NULL_ADDRESS):
            return None

        return address