fix: null pointer when source is null

Author: splincode

projects/table-builder/package.json

@@ -1,6 +1,6 @@
 {
     "name": "@angular-ru/ng-table-builder",
-    "version": "0.30.0",
+    "version": "0.31.0",
     "license": "MIT",
     "bugs": {
         "url": "https://github.com/Angular-RU/ng-table-builder/issues"

projects/table-builder/src/lib/table/directives/virtual-for.directive.ts

@@ -38,6 +38,10 @@ export class VirtualForDirective implements OnDestroy {
         this.createNewNodes(indexes);
     }
 
+    private get sourceRef(): TableRow[] {
+        return this._source || [];
+    }
+
     public ngOnDestroy(): void {
         this.view.clear();
         window.cancelAnimationFrame(this.createFrameId);
@@ -70,7 +74,7 @@ export class VirtualForDirective implements OnDestroy {
     }
 
     private createEmbeddedViewByIndex(index: VirtualIndex): void {
-        const row: TableRow = this._source[index.position];
+        const row: TableRow = this.sourceRef[index.position];
         const virtualRef: InternalVirtualRef = this.cache.get(index.position);
 
         if (virtualRef) {