docs: public VertexList vertexIds() {
          LongArrayList list = new LongArrayList();
          long previousId = 0;
          for (Long id : Iterables.transform(this,new Function<Entry, Long>() {
              @Nullable
              @Override
              public Long apply(@Nullable Entry entry) {
                  return edgeSerializer.readRelation(entry,true,tx).getOtherVertexId();
              }
          })) {
              list.add(id);
              if (id>=previousId && previousId>=0) previousId=id;
              else previousId=-1;
          }
          return new VertexLongList(tx,list,previousId>=0);
      }