while (iterator.hasNext()) {
          Entry<R, Map<C, V>> entry = iterator.next();
          if (entry.getValue().containsKey(columnKey)) {
            @WeakOuter
            final class EntryImpl extends AbstractMapEntry<R, V> {
              @Override
              public R getKey() {
                return entry.getKey();
              }

              @Override
              public V getValue() {