Marcel Taeumel uploaded a new version of Kernel to project The Trunk:
http://source.squeak.org/trunk/Kernel-mt.1014.mcz

==================== Summary ====================

Name: Kernel-mt.1014
Author: mt
Time: 12 April 2016, 6:54:04.593201 pm
UUID: b82ee689-f086-bc41-a438-f9c5b7e383c9
Ancestors: Kernel-mt.1013

Fixes uni-class clean-up by adding the check for #isSystemDefinied.

=============== Diff against Kernel-mt.1013 ===============

Item was changed:
  ----- Method: ClassDescription>>removeUninstantiatedSubclassesSilently (in category 'accessing class hierarchy') -----
  removeUninstantiatedSubclassesSilently
  	"Remove the classes of any subclasses that have neither instances nor subclasses.  Answer the number of bytes reclaimed"
+ 	"self removeUninstantiatedSubclassesSilently"
- 	"Player removeUninstantiatedSubclassesSilently"
  
+ 	| oldFree |
- 	| candidatesForRemoval  oldFree |
- 
  	oldFree := Smalltalk garbageCollect.
+ 	
+ 	self subclasses
+ 		select: [:c | (c isSystemDefined not and: [c instanceCount = 0]) and: [c subclasses isEmpty]]
+ 		thenDo: [:c | c removeFromSystem].
+ 	
+ 	^ Smalltalk garbageCollect - oldFree!
- 	candidatesForRemoval :=
- 		self subclasses select: [:c |
- 			(c instanceCount = 0) and: [c subclasses size = 0]].
- 	candidatesForRemoval do: [:c | c removeFromSystem].
- 	^Smalltalk garbageCollect - oldFree!