Why NameValueCollection instance initialization still compiles with extra comma?

Question

I am using NameValueCollection to store values that I will post to API server later. Today I accidentally added extra comma when I initialize an instance of NameValueCollection like simple code below:

NameValueCollection nvc = new NameValueCollection()
{
    ["foo"] = "bar",
    ["hello"] = "world", // <-- an extra comma here
};

Note that there is extra comma after world value. This code compiles normally on my computer and other dev's computer, with or without extra comma. But I can't manage it to run on .NET Fiddle even using the right code. I'm using .NET 4.6.1 if it matters.

I am aware of different way to initialize NameValueCollection like on fiddle above, but it's not the problem/question. My question is, why can the compiler compile this broken code and not issue some warning? Or maybe my Visual Studio settings are incorrect in somewhere? Or I am missing some coding principle? Please advice. Thank you.

Answer 1

1. This is not specific to NameValueCollection, all collection types as well as Enums allow this.
2. This has got nothing to do with .NET Framework version. This is a C# compiler feature.
3. This makes programmer's life easier. If you get a chance to work in PHP/JS, this feels like a welcome little feature.
4. You can read more details about it in this excellent SO post.