public static IAsyncEnumerable <TSource> DefaultIfEmpty <TSource>(this IAsyncEnumerable <TSource> source, TSource defaultValue) => LinqEnumerable.DefaultIfEmpty(source, defaultValue);
public static IAsyncEnumerable <TSource> DefaultIfEmpty <TSource>(this IAsyncEnumerable <TSource> source, TSource defaultValue) => LinqEnumerable.DefaultIfEmpty(source, defaultValue);