为什么在angular6的ng-multiselect-dropdown中没有定义idField？

<ng-multiselect-dropdown
  [placeholder]="'Select Countries'"
  formControlName="countries"
  id="multiSelect"
  [settings]="dropdownSettings"
  [data]="countriesList"
  (onSelect)="onItemSelect($event)"
  (onDeSelect)="onItemDeSelect($event)">
</ng-multiselect-dropdown>

export class YourComponent {
  countriesList = [
    { id: 1, name: 'India' },
    { id: 2, name: 'USA' },
    { id: 3, name: 'Canada' },
    // 其他国家
  ];

  dropdownSettings = {
    singleSelection: false,
    idField: 'id', // 定义idField
    textField: 'name',
    selectAllText: 'Select All',
    unSelectAllText: 'UnSelect All',
    itemsShowLimit: 3,
    allowSearchFilter: true
  };

  onItemSelect(item: any) {
    console.log('Item selected', item);
  }

  onItemDeSelect(item: any) {
    console.log('Item deselected', item);
  }
}