src/java.base/share/classes/java/util/concurrent/ConcurrentSkipListMap.java

*** 1127,1136 ****
--- 1127,1137 ----
                  (ConcurrentSkipListMap<K,V>) super.clone();
              clone.keySet = null;
              clone.entrySet = null;
              clone.values = null;
              clone.descendingMap = null;
+             clone.adder = null;
              clone.buildFromSorted(this);
              return clone;
          } catch (CloneNotSupportedException e) {
              throw new InternalError();
          }