g-type-string: return nil if type is invalid

diff --git a/glib/gobject.type-designator.lisp b/glib/gobject.type-designator.lisp
index a4b2bdf..d95e9b2 100644 (file)
--- a/glib/gobject.type-designator.lisp
+++ b/glib/gobject.type-designator.lisp
@@ -35,7 +35,7 @@ Numeric identifier of GType may be different between different program runs. But
 
 (defun g-type-string (g-type-designator)
   (etypecase g-type-designator
-    (string g-type-designator)
+    (string (g-type-name g-type-designator))
     (integer (g-type-name g-type-designator))
     (null nil)))