throw new IllegalArgumentException(
                "Overflow adding " + occurrences + " occurrences to a count of " + oldValue);
          }
        } else {
          // In the case of a concurrent remove, we might observe a zero value, which means another
          // thread is about to remove (element, existingCounter) from the map. Rather than wait,
          // we can just do that work here.

            throw new IllegalArgumentException(
                "Overflow adding " + occurrences + " occurrences to a count of " + oldValue);
          }
        } else {
          // In the case of a concurrent remove, we might observe a zero value, which means another
          // thread is about to remove (element, existingCounter) from the map. Rather than wait,
          // we can just do that work here.