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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_fwl_billing_item(self, firewall_id, dedicated=False):
 """Retrieves the billing item of the firewall. :param int firewall_id: Firewall ID to get the billing item for :param bool dedicated: whether the firewall is dedicated or standard :returns: A dictionary of the firewall billing item. """


        mask = 'mask[id,billingItem[id]]'
        if dedicated:
            firewall_service = self.client['Network_Vlan_Firewall']
        else:
            firewall_service = self.client['Network_Component_Firewall']
        firewall = firewall_service.getObject(id=firewall_id, mask=mask)
        if firewall is None:
            raise exceptions.SoftLayerError(
                "Unable to find firewall %d" % firewall_id)
        if firewall.get('billingItem') is None:
            raise exceptions.SoftLayerError(
                "Unable to find billing item for firewall %d" % firewall_id)

        return firewall['billingItem']