linkedSignal typed returning error due to being undefined

I have the following:

type TSelectOptions = {
badge?: StringType
disabled: boolean
expanded?: BooleanType
group?: string | undefined
icon?: StringType
id: TID
image?: StringType
index?: NumberType
info?: ArrayType<string>
iso?: ArrayType<string>
key: string
items: TSelectItem[]
selected?: boolean
value: string // number | string
view?: StringType
}

export type TSelectItem = {
id: TID
disabled?: boolean
emoji?: string
icon?: string
iso?: string
key?: string
selected?: boolean
value: string
view: string
}

export class SelectItem {
id: TID = ID()

disabled = false
emoji = ''
icon = ''
selected = false
view = ''
value = ''
}

export type TSelectItemGroup = TSelectItem & Pick<TSelectOptions, 'items'>
// Pick<TSelectOptions, 'key' | 'icon' | 'items' | 'selected'>



$titlesResrc: ResourceRef<TSelectItemGroup[]> = this.#resrcFacade.configureResource(
'registration',
'titles.json'
)


$titles: WritableSignal<TSelectItemGroup[]> = signal<TSelectItemGroup[]>([])

protected $titlesinked = linkedSignal({
source: (): ResourceRef<TSelectItemGroup[]> => this.$titlesResrc,
computation: () =>this.$titles.set( this.$titlesResrc ? this.$titlesResrc.value() : [])
})



The last line in $titlesLinked property:

computation: () =>this.$titles.set( this.$titlesResrc ? this.$titlesResrc.value() : [])


always results in the following error:

- error TS2345: Argument of type 'TSelectItemGroup[] | undefined' is not assignable to parameter of type 'TSelectItemGroup[]'.
Type 'undefined' is not assignable to type 'TSelectItemGroup[]'.

165 computation: () =>this.$titles.set( this.$titlesResrc ? this.$titlesResrc.value() : [])



I need some help in previnting the initial undefined which seems to generate the problem.

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