--- a/src/java.base/share/classes/java/util/concurrent/ConcurrentSkipListMap.java	Thu May 02 11:55:16 2019 +0100
+++ b/src/java.base/share/classes/java/util/concurrent/ConcurrentSkipListMap.java	Thu May 02 06:33:28 2019 -0700
@@ -1129,6 +1129,7 @@
             clone.entrySet = null;
             clone.values = null;
             clone.descendingMap = null;
+            clone.adder = null;
             clone.buildFromSorted(this);
             return clone;
         } catch (CloneNotSupportedException e) {