Trailing commas in constructor arguments?

[Gary Willoughby via Digitalmars-d-learn]

In the following snippet is the line marked WOAH legal? The 
compiler doesn't complain about the trailing comma in the 
constructor arguments.

import std.stdio;
class Foo
{
        public this(string foo)
        {
        }
}

void main(string[] args)
{
        auto foo = new Foo("bar", ); // <-- WOAH
}