--- a/HistoryManager.st	Wed Sep 07 21:27:56 2011 +0200
+++ b/HistoryManager.st	Wed Sep 07 21:39:22 2011 +0200
@@ -630,7 +630,9 @@
                 "/ same structure?
                 oldTree := RBParser parseMethod:oldSourceWithoutHistory onError:[:aString :pos | nil].
                 newTree := RBParser parseMethod:newSourceWithoutHistory onError:[:aString :pos | nil].
-                (oldTree equalTo:newTree withMapping:(renamedVariables := Dictionary new)) ifTrue:[
+                (oldTree notNil 
+                and:[newTree notNil
+                and:[oldTree equalTo:newTree withMapping:(renamedVariables := Dictionary new)]]) ifTrue:[
                     "/ only formatting?
                         (renamedVariables keysAndValuesSelect:[:k :v | k ~= v]) isEmpty ifTrue:[
                         "/ only formatting...
@@ -1000,7 +1002,7 @@
 !
 
 version
-    ^ '$Header: /cvs/stx/stx/libbasic3/HistoryManager.st,v 1.80 2011-07-20 18:19:42 cg Exp $'
+    ^ '$Header: /cvs/stx/stx/libbasic3/HistoryManager.st,v 1.81 2011-09-07 19:39:22 cg Exp $'
 ! !
 
 !HistoryManager::HistoryLine class methodsFor:'filtering'!
@@ -1695,7 +1697,7 @@
 !HistoryManager class methodsFor:'documentation'!
 
 version_CVS
-    ^ '$Header: /cvs/stx/stx/libbasic3/HistoryManager.st,v 1.80 2011-07-20 18:19:42 cg Exp $'
+    ^ '$Header: /cvs/stx/stx/libbasic3/HistoryManager.st,v 1.81 2011-09-07 19:39:22 cg Exp $'
 ! !
 
 HistoryManager initialize!