wow!
I upvoted this as best pratices, but not because I think it's a best practice, but so that more people will see it.

Huh, nice. First C# problem that I matched with the top solution. Was pretty weird coming from python and C and having to learn all of the built in methods again.

You know, magic ¯_(ツ)_/¯

how did six people use the same names and stuff and then get best practices?

Yes, it is irrelevant in this example. I'm guessing the kata is judged just by the structure of the function.

why does "Using System;" make this solution the best?

Thanks, I already understood that it is better not to do this.

You forked another user's translation and all the credit goes to them.

It is my C# translation
Why was my solution written to another person? Not fair.

Added call to Hello() with default arguments.
Removed test with null.

It's not a good idea to do this in C#.

Without any reason, this statement is meaningless.

Whether you like it or not, the original kata version expected the use of default arguments, and all languages where those are supported should comply with this.

It's not a good idea to do this in C#.

or says "Hello, World!" if name is not given (or passed as an empty String).

In some languages where default arguments are supported "name is not given" is tested by calling hello without any arguments. IMO, this is a better approach than calling it with null like you do here.

Please review and approve.

@author: are you still willing to solve the open issues?