@NotNull
  private GraphEdges getNeighborU(int rowIndex) {
    int upNeighborIndex = getUpNeighborIndex(rowIndex);
    GraphEdges graphEdges = cacheNU.get(upNeighborIndex);
    if (graphEdges == null) {
      graphEdges = getUCorrectEdges(upNeighborIndex);
      cacheNU.put(upNeighborIndex, graphEdges);
    }
    return graphEdges.copyInstance();
  }
@NotNull
  private GraphEdges getNeighborU(int rowIndex)