[Vala] poppler binding problems

[Rumen Zarev <rumen coding gmail com>]

I'm learning vala and was playing with some code using poppler. I found 
the following problem.

The type PopplerAction is defined in poppler-glib a union of ActionAny, 
ActionUri, and several others. The Vala bindings are:
    [Compact]
    [CCode (copy_function = "poppler_action_copy", type_id = 
"POPPLER_TYPE_ACTION", cheader_filename = "poppler.h")]
    public class Action {
        public weak Poppler.ActionAny any;
        public weak Poppler.ActionGotoDest goto_dest;
        public weak Poppler.ActionGotoRemote goto_remote;
        public weak Poppler.ActionLaunch launch;
        public weak Poppler.ActionMovie movie;
        public weak Poppler.ActionNamed named;
        public Poppler.ActionType type;
        public weak Poppler.ActionUri uri;
        public Poppler.Action copy ();
    }
    [Compact]
    [CCode (cheader_filename = "poppler.h")]
    public class ActionAny {
        public weak string title;
        public Poppler.ActionType type;
    }
etc.

I have the following code:
    Action action = ...
    stdout.printf(action.any.title);
This compiles to C code:
   fprintf(stdout, action->any->title);
which gives a gcc error.

If I use
    stdout.printf((ActionAny) action).title);
this compiles to the correct C code
    fprintf(stdout, ((PopplerActionAny *) action)->title);

Since I'm just starting to use vala, I don't know if that's a problem 
with the binding, or with the compiler. How does vala deal with unions 
in general?

-Rumen