Panic on unexpecting nil object

gir/girgen/types/typeconv/valueconverted.go

@@ -415,7 +415,13 @@ func (value *ValueConverted) cgoSetObject(conv *Converter) bool {
 		value.header.NeedsExternGLib()
 		value.p.Descend()
 		value.p.LineTmpl(m, `
-			object := externglib.<.Func>(unsafe.Pointer(<.Value.InPtr 1><.Value.InName>))
+			objptr := unsafe.Pointer(<.Value.InPtr 1><.Value.InName>)
+			<if not (or .Value.Optional .Value.Nullable) ->
+			if objptr == nil {
+				panic("object of type <.GoType> is nil")
+			}
+			<end>
+			object := externglib.<.Func>(objptr)
 			rv, ok := (<.Value.OutPtr 0>externglib.CastObject(object)).(<.Value.Out.Type>)
 			if !ok {
 				panic("object of type " + object.TypeFromInstance().String() + " is not <.GoType>")

pkg/core/glib/glib.go

@@ -455,6 +455,11 @@ func newObject(ptr unsafe.Pointer, take bool) *Object {
 
 // Cast casts v to the concrete Go type (e.g. *Object to *gtk.Entry).
 func (v *Object) Cast() Objector {
+	if v == nil {
+		// nil-typed interface != non-nil-typed nil-value interface
+		return nil
+	}
+
 	var gvalue C.GValue
 
 	C.g_value_init_from_instance(&gvalue, C.gpointer(v.Native()))