[shotwell] Fix warning when switching to faces page

[Jens Georg <jensgeorg src gnome org>]

commit 8fc08ad4edc86f46bee2b4994cae47b6751f331d
Author: Jens Georg <mail jensge org>
Date:   Mon Mar 18 15:21:27 2019 +0100

    Fix warning when switching to faces page

 src/faces/FacePage.vala | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/faces/FacePage.vala b/src/faces/FacePage.vala
index 31baa6b8..d238a5ae 100644
--- a/src/faces/FacePage.vala
+++ b/src/faces/FacePage.vala
@@ -77,7 +77,7 @@ public class FacePage : CollectionPage {
        
         menuFaces.add_menu_item(Resources.remove_face_from_photos_menu(this.face.get_name(), 
get_view().get_count()), "RemoveFaceFromPhotos", "<Primary>r");
         menuFaces.add_menu_item(Resources.rename_face_menu(this.face.get_name()), "RenameFace", 
"<Primary>e");
-        menuFaces.add_menu_item(Resources.set_face_from_photo_menu(this.face.get_name()), 
"SetFaceRefFromPhoto", "");
+        menuFaces.add_menu_item(Resources.set_face_from_photo_menu(this.face.get_name()), 
"SetFaceRefFromPhoto", null);
         menuFaces.add_menu_item(Resources.delete_face_menu(this.face.get_name()), "DeleteFace", 
"<Primary>t");
         
         return menuFaces;