Error in link data

Excuse me Walter, I got this Error tomorrow afternoon, of course before my code it ran
I used to this code
“myDiagram.model = go.Model.fromJson(
{
“nodeDataArray”: itemsIcon,
“linkDataArray”: itemsLink
}
)”
then it console.log() this Error
[ERROR Error: FromKey value for link data [object Object] is not a number or a string: null
at B (go.js:12)
at vq (go.js:1807)
at dr (go.js:1817)
at ar.set (go.js:1831)
at ar.push…/node_modules/gojs/release/go.js.t.Wv (go.js:1796)
at Function.push…/node_modules/gojs/release/go.js.Z.fromJSON.Z.fromJson (go.js:1778)
at DiagramViewComponent.push…/src/app/main/diagram/diagram-view/diagram-view.component.ts.DiagramViewComponent.loadServicesSuccess (diagram-view.component.ts:328)
at SafeSubscriber._next (diagram-view.component.ts:349)
at SafeSubscriber.push…/node_modules/rxjs/_esm5/internal/Subscriber.js.SafeSubscriber.__tryOrUnsub (Subscriber.js:196)
at SafeSubscriber.push…/node_modules/rxjs/_esm5/internal/Subscriber.js.SafeSubscriber.next (Subscriber.js:134)]

I am trying to use
“myDiagram.model.nodeDataArray = itemsIcon,
myDiagram.model.nodeDataArray = itemsLink”
It can show items, but my console.log() show this Error
ERROR Error: FromKey value for link data [object Object] is not a number or a string: null
at B (go.js:12)
at vq (go.js:1807)
at tq (go.js:1684)
at go.js:1683
at Array.forEach ()
at sq (go.js:1683)
at rq.push…/node_modules/gojs/release/go.js.rq.doModelChanged (go.js:1690)
at R.Y (go.js:570)
at ar.push…/node_modules/gojs/release/go.js.t.$s (go.js:1747)
at Wq (go.js:1748)

Although they work, I still want to know how to get rid of this Error
Please explain to me and How can I fix It, thanks, Sir

What is the value of itemsLink? And in particular, what is the link data object that causes that error?