How to get properties of nested objects with ng-multiselect-dropdown

Question

I'm trying to use the ng-multiselect-dropdown https://www.npmjs.com/package/ng-multiselect-dropdown. I've got an array, that contains nested objects. The structure looks some kind like this:

obj1: {
  id: string;
  atr1: {
    atr2: string;
    atr3: string;
  }
}

My question:

How can I display for example atr2 in the dropdown-menu? This is my dropdown-setting:

dropdownSettingsProjectManagers: any = {
        singleSelection: false,
        idField: 'id',
        textField: 'atr1.atr2',      //? What do I have to put in here?
        showSelectedItemsAtTop: true,
        clearSearchFilter: true,
        allowSearchFilter: true,
        enableCheckAll: false,
        allowRemoteDataSearch: true
    };

Thanks, for every help.