*/
@ElementTypesAreNonnullByDefault
final class UndirectedMultiNetworkConnections<N, E>
    extends AbstractUndirectedNetworkConnections<N, E> {

  private UndirectedMultiNetworkConnections(Map<E, N> incidentEdges) {
    super(incidentEdges);
  }

  static <N, E> UndirectedMultiNetworkConnections<N, E> of() {
    return new UndirectedMultiNetworkConnections<>(
        new HashMap<E, N>(INNER_CAPACITY, INNER_LOAD_FACTOR));
  }

        ? allowsParallelEdges()
            ? DirectedMultiNetworkConnections.<N, E>of()
            : DirectedNetworkConnections.<N, E>of()
        : allowsParallelEdges()
            ? UndirectedMultiNetworkConnections.<N, E>of()
            : UndirectedNetworkConnections.<N, E>of();
  }

    } else {
      Map<E, N> incidentEdgeMap =
          Maps.asMap(network.incidentEdges(node), adjacentNodeFn(network, node));
      return network.allowsParallelEdges()
          ? UndirectedMultiNetworkConnections.ofImmutable(incidentEdgeMap)
          : UndirectedNetworkConnections.ofImmutable(incidentEdgeMap);
    }
  }

  private static <N, E> Function<E, N> sourceNodeFn(Network<N, E> network) {