occurrencesLeft = currentEntry.getValue().get();
      }
      occurrencesLeft--;
      canRemove = true;
      /*
       * requireNonNull is safe because occurrencesLeft starts at 0, forcing us to initialize
       * currentEntry above. After that, we never clear it.
       */
      return requireNonNull(currentEntry).getKey();
    }

    @Override
    public void remove() {