Prevent passing null pointers when not nullable.
The arg-cache marshaller for null (pointers) doesn't check if the argument is nullable. This is a regression introduced by the arg-cache that can cause segfaults in functions such as GLib.str_hash.
The arg-cache marshaller for null (pointers) doesn't check if the argument is nullable. This is a regression introduced by the arg-cache that can cause segfaults in functions such as GLib.str_hash.