fix: rootKey empty check by len equals 0 (backport: cosmos#801) (cosmos#808)

Co-authored-by: Marko <marbar3778@yahoo.com>

Author: mmsqe

CHANGELOG.md

@@ -8,6 +8,10 @@
 - [#726](https://github.com/cosmos/iavl/pull/726) Make `KVPair` and `ChangeSet` serializable with protobuf.
 - [#795](https://github.com/cosmos/iavl/pull/795) Use gogofaster buf plugin.
 
+### Bug Fixes
+
+- [#801](https://github.com/cosmos/iavl/pull/801) Fix rootKey empty check by len equals 0.
+
 ## 0.20.0 (March 14, 2023)
 
 - [#622](https://github.com/cosmos/iavl/pull/622) `export/newExporter()` and `ImmutableTree.Export()` returns error for nil arguements

iterator.go

@@ -269,7 +269,7 @@ type NodeIterator struct {
 
 // NewNodeIterator returns a new NodeIterator to traverse the tree of the root node.
 func NewNodeIterator(rootKey []byte, ndb *nodeDB) (*NodeIterator, error) {
-	if rootKey == nil {
+	if len(rootKey) == 0 {
 		return &NodeIterator{
 			nodesToVisit: []*Node{},
 			ndb:          ndb,

iterator_test.go

@@ -330,3 +330,13 @@ func setupUnsavedFastIterator(t *testing.T, config *iteratorTestConfig) (dbm.Ite
 	itr := NewUnsavedFastIterator(config.startIterate, config.endIterate, config.ascending, tree.ndb, tree.unsavedFastNodeAdditions, tree.unsavedFastNodeRemovals)
 	return itr, mirror
 }
+
+func TestNodeIterator_WithEmptyRoot(t *testing.T) {
+	itr, err := NewNodeIterator(nil, newNodeDB(dbm.NewMemDB(), 0, nil))
+	require.NoError(t, err)
+	require.False(t, itr.Valid())
+
+	itr, err = NewNodeIterator([]byte{}, newNodeDB(dbm.NewMemDB(), 0, nil))
+	require.NoError(t, err)
+	require.False(t, itr.Valid())
+}