this.predecessorCount = checkNonNegative(predecessorCount);
    this.successorCount = checkNonNegative(successorCount);
    checkState(
        predecessorCount <= adjacentNodeValues.size()
            && successorCount <= adjacentNodeValues.size());
  }

  static <N, V> DirectedGraphConnections<N, V> of(ElementOrder<N> incidentEdgeOrder) {
    // We store predecessors and successors in the same map, so double the initial capacity.