Multiple asset selector.
type AssetsField<T extends Record<string, any> = Record<string, never>> = AssetField<T>[] | [];
type FeaturedImage = AssetsField<{ caption: string; credits: string }>;
// Result: {
// alt: string | null;
// height: number;
// id: string;
// permalink: string | null;
// width: number;
// caption: string;
// credits: string;
// }[] | []