EmptyDictionary<TKey, TValue>
sealed class EmptyDictionary<TKey, TValue> : IReadOnlyDictionary<TKey, TValue>, IEnumerable<KeyValuePair<TKey, TValue>>, IEnumerable, IReadOnlyCollection<KeyValuePair<TKey, TValue>>
DotNext
by .NET Foundation and Contributors
<PackageReference Include="DotNext" Version="4.13.0" />