[@fluentui/react-northstar] How to work with ShorthandValue

[diabhoil]

Hey,

maybe this is a stupid question but how can I work with ShorthandValues?

Lets say I have something like this:
let defaultVal: ShorthandValue<DropdownItemProps> = getMeAValueFromSomewhere();

How can I access for example the "header" or "selected" value of the DropdownItemProps now? VSCode says
Property 'selected' does not exist on type 'ShorthandValue<DropdownItemProps>'. Property 'selected' does not exist on type 'string'.ts(2339)

Is my tsconfig somehow wrong? Am I missing any types? Or do I have to convert the value to something useful before like this?
(defaultVal as DropdownItemProps).selected = true;

For some reason my searchable dropdown is not showing any default value, and cant even set the defaultSearchQuery parameter since I cant access the header value. Any help is appreciated!