channeldb/invoices: ignore error when no settles exist

This fixes a bug that would cause no backlog to be delivered at all.

channeldb/invoice_test.go

@@ -11,6 +11,7 @@ import (
 	"github.com/lightningnetwork/lnd/lntypes"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/record"
+	"github.com/stretchr/testify/assert"
 )
 
 var (
@@ -305,6 +306,9 @@ func TestInvoiceAddTimeSeries(t *testing.T) {
 		t.Fatalf("unable to make test db: %v", err)
 	}
 
+	_, err = db.InvoicesAddedSince(0)
+	assert.Nil(t, err)
+
 	// We'll start off by creating 20 random invoices, and inserting them
 	// into the database.
 	const numInvoices = 20
@@ -372,6 +376,9 @@ func TestInvoiceAddTimeSeries(t *testing.T) {
 		}
 	}
 
+	_, err = db.InvoicesSettledSince(0)
+	assert.Nil(t, err)
+
 	var settledInvoices []Invoice
 	var settleIndex uint64 = 1
 	// We'll now only settle the latter half of each of those invoices.

channeldb/invoices.go

@@ -488,12 +488,12 @@ func (d *DB) InvoicesAddedSince(sinceAddIndex uint64) ([]Invoice, error) {
 	err := kvdb.View(d, func(tx kvdb.ReadTx) error {
 		invoices := tx.ReadBucket(invoiceBucket)
 		if invoices == nil {
-			return ErrNoInvoicesCreated
+			return nil
 		}
 
 		addIndex := invoices.NestedReadBucket(addIndexBucket)
 		if addIndex == nil {
-			return ErrNoInvoicesCreated
+			return nil
 		}
 
 		// We'll now run through each entry in the add index starting
@@ -520,12 +520,7 @@ func (d *DB) InvoicesAddedSince(sinceAddIndex uint64) ([]Invoice, error) {
 
 		return nil
 	})
-	switch {
-	// If no invoices have been created, then we'll return the empty set of
-	// invoices.
-	case err == ErrNoInvoicesCreated:
-
-	case err != nil:
+	if err != nil {
 		return nil, err
 	}
 
@@ -886,12 +881,12 @@ func (d *DB) InvoicesSettledSince(sinceSettleIndex uint64) ([]Invoice, error) {
 	err := kvdb.View(d, func(tx kvdb.ReadTx) error {
 		invoices := tx.ReadBucket(invoiceBucket)
 		if invoices == nil {
-			return ErrNoInvoicesCreated
+			return nil
 		}
 
 		settleIndex := invoices.NestedReadBucket(settleIndexBucket)
 		if settleIndex == nil {
-			return ErrNoInvoicesCreated
+			return nil
 		}
 
 		// We'll now run through each entry in the add index starting