}

          // Mostly safe: We check contains(u) before calling successors(u), so we perform unsafe
          // operations only in weird cases like checking for an EndpointPair<ArrayList> in a
          // Network<LinkedList>.
          @SuppressWarnings("unchecked")
          @Override
          public boolean contains(@CheckForNull Object obj) {
            if (!(obj instanceof EndpointPair)) {
              return false;
            }