@Nullable Segment<K, V> currentSegment;
    @Nullable AtomicReferenceArray<ReferenceEntry<K, V>> currentTable;
    @Nullable ReferenceEntry<K, V> nextEntry;
    @Nullable WriteThroughEntry nextExternal;
    @Nullable WriteThroughEntry lastReturned;

    HashIterator() {
      nextSegmentIndex = segments.length - 1;
      nextTableIndex = -1;
      advance();
    }

    @Override