[Vala] Array as generic type not allowed? Can't ArrayList<string[]>

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I tried to create a list of string[] but it's not allowed on vala 
version 0.16.1.

using Gee;
void main() {
    var strings_list = new ArrayList<string[]>();
}

gives:
error: `string[]' is not a supported generic type argument, use `?' to 
box value types

And adding "?" still give the same error.

Should generic support array as a type? Is it a bug?