fn get_update_fulfill_htlc(&mut self, htlc_id_arg: u64, payment_preimage_arg: PaymentPreimage) -> Result<(Option<msgs::UpdateFulfillHTLC>, Option<ChannelMonitorUpdate>), ChannelError> {
// Either ChannelFunded got set (which means it won't be unset) or there is no way any
// caller thought we could have something claimed (cause we wouldn't have accepted in an
fn get_update_fulfill_htlc(&mut self, htlc_id_arg: u64, payment_preimage_arg: PaymentPreimage) -> Result<(Option<msgs::UpdateFulfillHTLC>, Option<ChannelMonitorUpdate>), ChannelError> {
// Either ChannelFunded got set (which means it won't be unset) or there is no way any
// caller thought we could have something claimed (cause we wouldn't have accepted in an