Fix GetSiblingNode

deepsubtree.go

@@ -62,7 +62,7 @@ func (tree *ImmutableTree) GetSiblingNode(key []byte) (*Node, error) {
 
 func (tree *ImmutableTree) recursiveGetSiblingNode(node *Node, key []byte) (*Node, error) {
 	if node == nil || node.isLeaf() {
-		return nil, fmt.Errorf("no sibling node found for key: %s", key)
+		return nil, nil
 	}
 	leftNode, err := node.getLeftNode(tree)
 	if err != nil {
@@ -72,14 +72,19 @@ func (tree *ImmutableTree) recursiveGetSiblingNode(node *Node, key []byte) (*Nod
 	if err != nil {
 		return nil, err
 	}
-	if leftNode != nil && bytes.Equal(leftNode.key, key) {
+	if leftNode != nil && leftNode.isLeaf() && bytes.Equal(leftNode.key, key) {
 		return rightNode, nil
 	}
-	if rightNode != nil && bytes.Equal(rightNode.key, key) {
+	if rightNode != nil && rightNode.isLeaf() && bytes.Equal(rightNode.key, key) {
 		return leftNode, nil
 	}
-	if bytes.Compare(node.key, key) < 0 {
-		return tree.recursiveGetSiblingNode(leftNode, key)
+
+	siblingNode, err := tree.recursiveGetSiblingNode(leftNode, key)
+	if err != nil {
+		return nil, err
+	}
+	if siblingNode != nil {
+		return siblingNode, nil
 	}
 	return tree.recursiveGetSiblingNode(rightNode, key)
 }