"Attempt to read property "resourceClass" on null" about nova-multiselect-field HOT 5 CLOSED

$withTrashed = $this->shouldIncludeTrashed(
  $request, $associatedResource = $field->resourceClass
);

    public function fields(NovaRequest $request)
    {
        return [
            Text::make('Name')->rules('required'),
            Number::make('Validity in days', 'validity_in_days')->rules('required'),
            Date::make('Activated At', 'activated_at')->readonly()->hideWhenCreating()->hideWhenUpdating(),
            Date::make('Expires At', 'expires_at')->readonly()->hideWhenCreating()->hideWhenUpdating(),
            BelongsTo::make('Tenant')->DisplayUsing(function ($tenant) {
                return $tenant->msp_name . ' (' . $tenant->id . ')';
            })->rules('required'),
            Multiselect::make('Standards', 'standards')
            ->belongsToMany(\App\Nova\Central\Standard::class, false),
        ];
    }