--- a/UndefinedObject.st	Sun Jul 16 14:22:58 2017 +0200
+++ b/UndefinedObject.st	Mon Jul 17 11:42:28 2017 +0200
@@ -110,7 +110,6 @@
     "Modified: 3.1.1997 / 15:06:15 / cg"
 ! !
 
-
 !UndefinedObject class methodsFor:'queries'!
 
 canBeSubclassed
@@ -154,8 +153,6 @@
 ! !
 
 
-
-
 !UndefinedObject methodsFor:'converting'!
 
 asBoolean
@@ -214,6 +211,23 @@
     ^ self
 ! !
 
+!UndefinedObject methodsFor:'debugging'!
+
+haltIfNil
+    "halt if the receiver is nil"
+
+    <resource: #skipInDebuggersWalkBack>
+
+    self halt:'nil encountered'
+
+    "
+     3 haltIfNil
+     nil haltIfNil
+    "
+
+    "Created: / 17-07-2017 / 10:52:36 / cg"
+! !
+
 !UndefinedObject methodsFor:'dependents access'!
 
 addDependent:someObject
@@ -307,7 +321,6 @@
     "Modified (comment): / 17-05-2017 / 16:37:19 / mawalch"
 ! !
 
-
 !UndefinedObject methodsFor:'subclass creation'!
 
 nilSubclass:action
@@ -741,7 +754,6 @@
     ^ aVisitor visitNilWith:aParameter
 ! !
 
-
 !UndefinedObject class methodsFor:'documentation'!
 
 version