[Vala] strict non-null check

[Luca Dionisi <luca dionisi gmail com>]

When passing a non-null object to a function, valac will put this check:
  g_return_if_fail (v != NULL);

So, if I pass a null value the function is not performed, a message is
printed and the rest of the application happily carries on.

How can I make the program to abort when a null is passed to a non-null object?

TIA
--Luca