Issue when droping the shape from the flyout the 2nd time

I was trying to put the shape from the flyout…1st time it was sucessfull…2nd time when I try it throws an error “ERROR TypeError: Cannot set property ‘isSelected’ of null”…Pasting the code below

      const pointtoreduce = 42;
      const mx = event.clientX - pointtoreduce;
      const my = event.clientY - pointtoreduce;
      const point = this.myDiagram.transformViewToDoc(new go.Point(mx, my));
      const droptoPart = this.myDiagram.findPartAt(point, false);
      console.log('droptoPart', droptoPart);
      const node = this.getNodeFromGroupButton(this.toolbarService.selectedGroup);
      if (undefined !== node) {
        delete node['__gohashid'];
        if (droptoPart instanceof go.Group) {
          node['group'] = droptoPart.data.key;
        }
        this.myDiagram.startTransaction('new node');
        if (node['category'] === 'Pool') {
          this.createPool(node, point);
        } else if (node['category'] === 'subprocess') {
          this.createSubprocess(node, point);
        } else {
          node['key'] = this.getKey(node['key']);
          node['loc'] = `${point.x}` + `${' '}` + `${point.y}`;
          this.myDiagram.model.addNodeData(node);
          console.log('this.myDiagram.findNodeForKey', node['key']);
         // console.log('this.myDiagram.model.addNodeData(node)', this.myDiagram.model.addNodeData(node));
          this.myDiagram.findNodeForKey(node['key']).isSelected = true;
          //console.log('this.myDiagram.findNodeForKey', node['key']);
          this.myDiagram.select(this.myDiagram.findNodeForKey(node['key']));
        }
        this.myDiagram.commitTransaction('new node');
        this.createprops(this.myDiagram.findNodeForKey(node['key']));
      }
      this.myDiagram.commandHandler.diagram.doFocus();
    }, false);

    this.myDiagram.addDiagramListener('SelectionCopied', () => {
      this.relayoutDiagramEx(this._self);
    });
    this.createDummyNode();
  }```

please look into the code and give me a solution.The code of "getNodeFromGroupButton" is given below:

```private getNodeFromGroupButton(selectedGroup: string): object {
    let node;
    switch (selectedGroup) {
      case 'start':
        node = this.toolbarService.startGroupNode.data;
        console.log('node',node);
        console.log('node stringfy',JSON.stringify(node));
        break;
      case 'intermediate':
        node = this.toolbarService.interMediateGroupNode.data;
        break;
      case 'end':
        node = this.toolbarService.endGroupNode.data;
        break;
      case 'task':
        node = this.toolbarService.taskGroupNode.data;
        break;
      case 'subprocess':
        node = this.toolbarService.subProcessGroupNode.data;
        break;
      case 'gateway':
        node = this.toolbarService.subProcessGroupNode.data;
        break;
      case 'artifacts':
        node = this.toolbarService.artifactGroupNode.data;
        break;
      case 'dataobject':
        node = this.toolbarService.dataGroupNode.data;
        break;
      default:
        break;
    }
    return node;
  }```

Don’t touch the __gohashid property!