diff --git a/src/components/flatTree/flatTree.component.ts b/src/components/flatTree/flatTree.component.ts
index d8cd1d832244fca9882eff9ecc18889a7d9bac79..ba6c13546925efa8aab616454280e3402c488230 100644
--- a/src/components/flatTree/flatTree.component.ts
+++ b/src/components/flatTree/flatTree.component.ts
@@ -48,6 +48,12 @@ export class FlatTreeComponent implements AfterViewChecked {
   uncollapsedLevels : Set<string> = new Set()
 
   ngAfterViewChecked(){
+    /**
+     * if useDefaultList is true, virtualscrollViewPort will be undefined
+     */
+    if (!this.virtualScrollViewPort) {
+      return
+    }
     const currentTotalDataLength = this.virtualScrollViewPort.getDataLength()
     const previousDataLength = this.totalDataLength