Stream throws

works.cs

using System;
using System.IO;

namespace ConsoleApp19
{
    class Program
    {
        static void Main(string[] args)
        {
            var ms = new MemoryStream();
            var source = new MyStream();
            source.CopyTo(ms);
        }
    }

    public class MyStream : Stream
    {
        public override bool CanRead => false;

        public override bool CanSeek => false;

        public override bool CanWrite => true;

        public override long Length => 0;

        public override long Position { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }

        public override void Flush()
        {
        }

        public override int Read(byte[] buffer, int offset, int count)
        {
            return 0;
        }

        public override long Seek(long offset, SeekOrigin origin)
        {
            return 0;
        }

        public override void SetLength(long value)
        {
        }

        public override void Write(byte[] buffer, int offset, int count)
        {
        }
    }
}