A static field with an object from some class is null when used in an other class. Here's an example:

public class Bar {

    public static /*const*/ Bar STATICBAR = new Bar ();
    
    public string printme { get; set; default = "bar"; }
}

public class Foo {

    public void func ( Bar bar ) {
        stdout.printf ( "%s", bar.printme );
    }

    public static int main ( string[] args ) {
        var c = new Foo ();
        c.func ( Bar.STATICBAR );
        return 0;
    }
}

The string is never printed as bar is null and the parameter assertion of the method func fails.

The code does work when the string printme and the static field are moved to the Foo class (so the static field then holds a Foo object).

I've commented const for STATICBAR as this causes the C code to be invalid (duplicate variables) but this has already been reported.