invoices: do not log when invoice is already deleted

docs/release-notes/release-notes-0.14.0.md

@@ -584,6 +584,9 @@ messages directly. There is no routing/path finding involved.
   re-notified](https://github.com/lightningnetwork/lnd/pull/5901), which could
   lead to higher-level HTLC mismanagement issues.
 
+* [Do not error log when an invoice that has been canceled and GC'd is expired](
+  https://github.com/lightningnetwork/lnd/pull/5913)
+
 ## Documentation 
 
 The [code contribution guidelines have been updated to mention the new

invoices/invoice_expiry_watcher.go

@@ -353,6 +353,11 @@ func (ew *InvoiceExpiryWatcher) expireInvoice(hash lntypes.Hash, force bool) {
 
 	case channeldb.ErrInvoiceAlreadySettled:
 
+	case channeldb.ErrInvoiceNotFound:
+		// It's possible that the user has manually canceled the invoice
+		// which will then be deleted by the garbage collector resulting
+		// in an ErrInvoiceNotFound error.
+
 	default:
 		log.Errorf("Unable to cancel invoice: %v: %v", hash, err)
 	}