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

  UndirectedNetworkConnections(Map<E, N> incidentEdgeMap) {
    super(incidentEdgeMap);
  }

  static <N, E> UndirectedNetworkConnections<N, E> of() {
    return new UndirectedNetworkConnections<>(HashBiMap.<E, N>create(EXPECTED_DEGREE));
  }

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