def is_forwarded_htlc(self, htlc_key) -> Optional[str]:
        """Returns whether this was a forwarded HTLC."""
        for payment_key, htlcs in self.active_forwardings.items():
            if htlc_key in htlcs:
                return payment_key
Returns whether this was a forwarded HTLC.
electrum/lnworker.py