Iterable<? extends T> a, Iterable<? extends T> b, Iterable<? extends T> c) {
    return concatNoDefensiveCopy(a, b, c);
  }

  /**
   * Returns a fluent iterable that combines four iterables. The returned iterable has an iterator
   * that traverses the elements in {@code a}, followed by the elements in {@code b}, followed by

      Iterable<? extends T> a, Iterable<? extends T> b, Iterable<? extends T> c) {
    return concatNoDefensiveCopy(a, b, c);
  }

  /**
   * Returns a fluent iterable that combines four iterables. The returned iterable has an iterator
   * that traverses the elements in {@code a}, followed by the elements in {@code b}, followed by

    GraphConnections<N, V> connectionsU = nodeConnections.get(nodeU);
    V value = (connectionsU == null) ? null : connectionsU.value(nodeV);
    // TODO(b/192579700): Use a ternary once it no longer confuses our nullness checker.
    if (value == null) {
      return defaultValue;
    } else {
      return value;
    }
  }