Socket.SendFile(string) argument is supposed to be nullable

[stephentoub]

The docs for Socket.SendFile(string) state that the string argument is allowed to be null, and on .NET Framework when it's null, the operation executes fine, sending nothing. However, in .NET 5 the string argument is annotated as non-nullable, and on Windows it throws an exception when null is provided, as in #42529.

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[wfurt]

I could see that it can be null if you can also pass in buffer but what do you expect to happen if you use overload just with the string name and that is not provided?

[stephentoub]

The same thing that happens on .NET Framework or if you use Socket.Send(new byte[0])... it sends nothing. I agree there's relatively little use in this, but it enables consistency with the SendFile overload that takes pre/post-buffers as well, and where null for the file stream makes more sense.