diff --git a/npm/ng-packs/packages/core/src/lib/utils/tree-utils.ts b/npm/ng-packs/packages/core/src/lib/utils/tree-utils.ts
index d4c0ba0ab3..ba6e3a5b90 100644
--- a/npm/ng-packs/packages/core/src/lib/utils/tree-utils.ts
+++ b/npm/ng-packs/packages/core/src/lib/utils/tree-utils.ts
@@ -1,7 +1,7 @@
 export class BaseTreeNode<T extends object> {
   children: TreeNode<T>[] = [];
   isLeaf = true;
-  parent: TreeNode<T>;
+  parent?: TreeNode<T>;
 
   constructor(props: T) {
     Object.assign(this, props);
@@ -14,7 +14,7 @@ export class BaseTreeNode<T extends object> {
 
 export function createTreeFromList<T extends object, R extends unknown>(
   list: T[],
-  keySelector: (item: T) => number | string | symbol,
+  keySelector: (item: T) => NodeKey,
   parentKeySelector: typeof keySelector,
   valueMapper: (item: T) => R,
 ) {
@@ -26,6 +26,8 @@ export function createTreeFromList<T extends object, R extends unknown>(
     const parentId = parentKeySelector(row);
     const node = map.get(id);
 
+    if (!node) return;
+
     if (parentId) {
       const parent = map.get(parentId);
       if (!parent) return;
@@ -42,7 +44,7 @@ export function createTreeFromList<T extends object, R extends unknown>(
 
 export function createMapFromList<T extends object, R extends unknown>(
   list: T[],
-  keySelector: (item: T) => number | string | symbol,
+  keySelector: (item: T) => NodeKey,
   valueMapper: (item: T) => R,
 ) {
   type Key = ReturnType<typeof keySelector>;
@@ -60,6 +62,8 @@ export type TreeNode<T extends object> = {
   parent?: TreeNode<T>;
 };
 
+type NodeKey = number | string | symbol | undefined | null;
+
 type NodeValue<T extends object, F extends (...args: any) => any> = F extends undefined
   ? TreeNode<T>
   : ReturnType<F>;