fix dock to

Author: jogibear9988

lib/js/webcomponent/DockSpawnTsWebcomponent.js

@@ -1,6 +1,6 @@
 {
   "name": "dock-spawn-ts",
-  "version": "3.8.3",
+  "version": "3.9.0",
   "description": "DockSpawn Typescript Version",
   "license": "MIT",
   "author": "[email protected]",

lib/js/webcomponent/DockSpawnTsWebcomponent.js.map

@@ -122,8 +122,10 @@ export class DockSpawnTsWebcomponent extends HTMLElement {
         let dockToAttribute = element.getAttribute('dock-spawn-dock-to');
         if (dockToAttribute) {
             //@ts-ignore
-            let dockToElement = this.getRootNode().getElementById(dockToAttribute) as HTMLElement;
-            dockRelativeTo = this.dockManager.findNodeFromContainerElement(this.elementContainerMap.get(dockToElement).containerElement);
+            const dockToElement = this.getRootNode().getElementById(dockToAttribute) as HTMLElement;
+            if (dockToElement) {
+                dockRelativeTo = this.dockManager.findNodeFromContainerElement(this.elementContainerMap.get(dockToElement).containerElement);
+            }
         }
 
         if (dockType == 'left')