Update README.md

Co-Authored-By: Vlad Rindevich <[email protected]>

Author: johannalee

README.md

@@ -260,8 +260,8 @@ function* treeWalker(refresh) {
         }
       : id;
 
-    if (children?.length !== 0 && isOpened) {
-      for (let i = children?.length - 1; i >= 0; i--) {
+    if (children && children.length !== 0 && isOpened) {
+      for (let i = children.length - 1; i >= 0; i--) {
         stack.push({
           nestingLevel: nestingLevel + 1,
           node: children[i],