What is the alternative of [clearable] in ng-selecr

Question

I do not want to use the [clearable] in ng-select for leakage of my space. Instead of [clearable] I want to use only [clearOnBackspace] but when I write [clearable] = "false" and [clearOnBackspace] = "true" it does not work.

enter code here

    <ng-select [items]="cities"
               bindLabel="name"
               placeholder="Select city"
               [(ngModel)]="selectedCity"
               [clearable]="false"
               [clearOnBackspace] = "true"
               [excludeGroupsFromDefaultSelection] = "true">
    </ng-select>