--- a/FileApplicationNoteBook.st	Wed Jan 20 23:57:35 2016 +0000
+++ b/FileApplicationNoteBook.st	Thu Jan 21 06:47:58 2016 +0100
@@ -4358,7 +4358,11 @@
 postOpenAsSubcanvasWith:aBuilder 
     "invoked if the application is embedded in some other view"
 
-    self imageView windowGroup addPreEventHook:self.
+    |wg|
+    
+    (wg := self imageView windowGroup) notNil ifTrue:[
+        wg addPreEventHook:self.
+    ].
     super postOpenAsSubcanvasWith:aBuilder
 !