@ElementTypesAreNonnullByDefault
abstract class EndpointPairIterator<N> extends AbstractIterator<EndpointPair<N>> {
  private final BaseGraph<N> graph;
  private final Iterator<N> nodeIterator;

  @CheckForNull
  N node = null; // null is safe as an initial value because graphs don't allow null nodes

  Iterator<N> successorIterator = ImmutableSet.<N>of().iterator();

  static <N> EndpointPairIterator<N> of(BaseGraph<N> graph) {

   */
  @Override
  public Set<EndpointPair<N>> edges() {
    return new AbstractSet<EndpointPair<N>>() {
      @Override
      public UnmodifiableIterator<EndpointPair<N>> iterator() {
        return EndpointPairIterator.of(AbstractBaseGraph.this);
      }

      @Override
      public int size() {
        return Ints.saturatedCast(edgeCount());
      }

      @Override