--- a/MultipleItemSelectionWidget.st	Mon May 30 09:41:17 2016 +0200
+++ b/MultipleItemSelectionWidget.st	Tue May 31 15:26:36 2016 +0200
@@ -363,19 +363,21 @@
 addItemsToSelection
     "add selected items from left list to the right list"
 
-    |sel t|
+    |sel t selectedItemList possibleItemList|
 
     sel := self possibleItemListSelection value.
-    sel size > 0 ifTrue:[
-	t := self listOfSelectedItems value copy.
-	t addAll:sel.
-	self listOfSelectedItems value:t.
+    sel notEmptyOrNil ifTrue:[
+        selectedItemList := self listOfSelectedItems. 
+        t := selectedItemList value copy.
+        t addAll:sel.
+        selectedItemList value:t.
 
-	t := self listOfPossibleItems value copy.
-	t removeAll:sel.
-	self listOfPossibleItems value:t.
+        possibleItemList := self listOfPossibleItems. 
+        t := possibleItemList value copy.
+        t removeAll:sel.
+        possibleItemList value:t.
 
-	self possibleItemListSelection value:#()
+        self possibleItemListSelection value:#()
     ]
 !
 
@@ -401,19 +403,21 @@
 removeItemsFromSelection
     "remove selected items from right list to the left list"
 
-    |sel t|
+    |sel t selectedItemList possibleItemList|
 
     sel := self selectedItemListSelection value.
     sel size > 0 ifTrue:[
-	t := self listOfPossibleItems value copy.
-	t addAll:sel.
-	self listOfPossibleItems value:t.
+        possibleItemList := self listOfPossibleItems. 
+        t := possibleItemList value copy.
+        t addAll:sel.
+        possibleItemList value:t.
 
-	t := self listOfSelectedItems value copy.
-	t removeAll:sel.
-	self listOfSelectedItems value:t.
+        selectedItemList := self listOfSelectedItems. 
+        t := selectedItemList value copy.
+        t removeAll:sel.
+        selectedItemList value:t.
 
-	self selectedItemListSelection value:#()
+        self selectedItemListSelection value:#()
     ]
 !