Incorrect optional typescript declaration generation?

Given following Motoko code:

actor Deck {
    private type DeckData = {
        header: ?Text;
    };
}

The SDK (v0.7.7) generates following type declaration:

export interface DeckData {
  'header' : [] | [string],
}

Isn’t that incorrect?

Shouldn’t be header?: string or header: string | null?