Marcel Taeumel uploaded a new version of System to project The Trunk:
http://source.squeak.org/trunk/System-mt.1028.mcz

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

Name: System-mt.1028
Author: mt
Time: 24 May 2018, 10:35:51.133621 am
UUID: e67895c1-7fda-a446-a702-5757e36441ec
Ancestors: System-mt.1027

Adds clean-up code for distinguished null-(class/method)-references.

=============== Diff against System-mt.1027 ===============

Item was added:
+ ----- Method: ClassReference class>>cleanUp: (in category 'class initialization') -----
+ cleanUp: aggressive
+ 
+ 	aggressive ifTrue: [InvalidReference := nil].!

Item was added:
+ ----- Method: MethodReference class>>cleanUp: (in category 'class initialization') -----
+ cleanUp: aggressive
+ 
+ 	aggressive ifTrue: [InvalidReference := nil].!