return empty list from getsubtreeaslist instead of error

src/ua/AddressSpace.ts

@@ -30,7 +30,7 @@ export class AddressSpace implements IAddressSpace{
     public getSubTreeAsList(nodeId: string): UABaseNode[] {
         const node=this.findNode(nodeId);
         if(!node)
-            throw new Error(`Nodeid ${nodeId} not found`)
+            return [];
         const nlist:UABaseNode[]=[node];
         for(const n of node.getChildren()) {
             const list=this.getSubTreeAsList(n.nodeId.toString());