Variable for selectionType with Typescript is broken

[elinake]

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[ ] feature request
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Current behavior

With typescript it is not possible to use a variable in selectionType, because "undefined", or "null" are not valid values.

Expected behavior

import { SelectionType } from '@swimlane/ngx-datatable';

  get selectionType(): SelectionType | undefined {
    return this.readOnly ? undefined  : SelectionType.checkbox;
  }

<ngx-datatable
  [selectionType]="selectionType"
>
</ngx-datatable>

This should be possible, but it is not.

Reproduction of the problem

Example plunker is not running at all so I can't reproduce the problem.

What is the motivation / use case for changing the behavior?

Nobody makes anything serious without typesafe code.

Please tell us about your environment:

• Table version: 20.1.0

• Angular version: 15.2.9

• Browser: all

• Language: TypeScript 4.9.4