--- old/src/java.base/share/classes/java/util/concurrent/ConcurrentSkipListMap.java	2019-04-24 17:10:48.370497103 +0100
+++ new/src/java.base/share/classes/java/util/concurrent/ConcurrentSkipListMap.java	2019-04-24 17:10:47.966487550 +0100
@@ -1129,6 +1129,7 @@
             clone.entrySet = null;
             clone.values = null;
             clone.descendingMap = null;
+            clone.adder = null;
             clone.buildFromSorted(this);
             return clone;
         } catch (CloneNotSupportedException e) {