C# Tiny HashSet

TinyHashSet.cs

[DebuggerTypeProxy(typeof(HashSetDebugViewInt<>))]
[DebuggerDisplay("Count = {Count}")]
[Serializable]
public class TinyHashSet<T> : TinySet<T>, IEnumerable<T>
{
    public TinyHashSet() : this(EqualityComparer<T>.Default)
    {
    }
    public TinyHashSet(IEqualityComparer<T> comparer)
    {
        if(Comparer == null)
            Comparer = EqualityComparer<T>.Default;
        Comparer = comparer;
    }
    public TinyHashSet(IEnumerable<T> collection)
    {
        Comparer = EqualityComparer<T>.Default;
        foreach(var item in collection)
            Add(item);
    }
    IEnumerator<T> IEnumerable<T>.GetEnumerator()
    {
        return new Enumerator(this);
    }
    IEnumerator IEnumerable.GetEnumerator()
    {
        return new Enumerator(this);
    }
    /// <summary>
    ///     Will not include duplicate entries.
    /// </summary>
    public void AddUnique(IEnumerable<T> collection)
    {
        foreach(var item in collection)
            Add(item);
    }
    public Enumerator GetEnumerator()
    {
        return new Enumerator(this);
    }
    [Serializable]
    public struct Enumerator : IEnumerator<T>
    {
        private readonly TinyHashSet<T> ths;
        private          int            index;
        public           T              Current{get; private set;}
        object IEnumerator.Current
        {
            get
            {
                if(index == 0 || index == ths.Count + 1)
                    throw new InvalidOperationException($"Enumerator out of range: {index}");
                return Current;
            }
        }
        internal Enumerator(TinyHashSet<T> set)
        {
            ths     = set;
            index   = 0;
            Current = default;
        }
        public void Dispose()
        {
        }
        public bool MoveNext()
        {
            if(index < ths.Count)
            {
                Current = ths.Slots[index].Value;
                index++;
                return true;
            }
            index   = ths.Count + 1;
            Current = default;
            return false;
        }
        void IEnumerator.Reset()
        {
            index   = 0;
            Current = default;
        }
    }
}