T290 Issues: Value cannot be null. Parameter name: key. Does anyone know the flaw in this sample code?

RS201000.ts codes:

import {

    PXScreen, graphInfo, createCollection,

    PXView,PXFieldState,

    gridConfig,PXFieldOptions,GridPreset

 } from "client-controls";

@gridConfig({

    preset:GridPreset.Primary

})

export class RSSVRepairService extends PXView

{

    ServiceCD : PXFieldState;

    Description : PXFieldState;

    Active : PXFieldState;

    WalkInService : PXFieldState<PXFieldOptions.CommitChanges>;

    Prepayment : PXFieldState;

    PreliminaryCheck : PXFieldState<PXFieldOptions.CommitChanges>;

}

@graphInfo({

    graphType:"PhoneRepairShop.RSSVRepairServiceMaint",

    primaryView:"RepairService",

    hideFilesIndicator:true,

    hideNotesIndicator:true

})

export class RS201000 extends PXScreen{

    RepairService=createCollection(RSSVRepairService)

}

RS201000.html Codes:

<template>

    <qp-grid id="grid-RepairService" view-bind="RepairService"></qp-grid>

</template>