Dotnet_Library/project_name/HelloWorldProvider.cs

namespace project_name;

public class HelloWorldProvider
{
    public string GetHelloWorld(string? name = null)
    {
        if (string.IsNullOrEmpty(name))
        {
            return "Hello world!";
        }
        else
        {
            return $"Hello, {name}!";
        }
    }
}