Iterator<? extends T> a,
      Iterator<? extends T> b,
      Iterator<? extends T> c,
      Iterator<? extends T> d) {
    checkNotNull(a);
    checkNotNull(b);
    checkNotNull(c);
    checkNotNull(d);
    return concat(consumingForArray(a, b, c, d));
  }

  /**
   * Combines multiple iterators into a single iterator. The returned iterator iterates across the

      Iterator<? extends T> a,
      Iterator<? extends T> b,
      Iterator<? extends T> c,
      Iterator<? extends T> d) {
    checkNotNull(a);
    checkNotNull(b);
    checkNotNull(c);
    checkNotNull(d);
    return concat(consumingForArray(a, b, c, d));
  }

  /**
   * Combines multiple iterators into a single iterator. The returned iterator iterates across the

    }
  }

  /*
   * Preconditions.checkNotNull is *intended* for performing eager null checks on parameters that a
   * nullness checker can already "prove" are non-null. That means that the first parameter to
   * checkNotNull *should* be annotated to require it to be non-null.
   *

  }

  @Override
  public T or(T defaultValue) {
    return checkNotNull(defaultValue, "use Optional.orNull() instead of Optional.or(null)");
  }

  @SuppressWarnings("unchecked") // safe covariant cast
  @Override
  public Optional<T> or(Optional<? extends T> secondChoice) {
    return (Optional<T>) checkNotNull(secondChoice);
  }

  @Override
  public T or(Supplier<? extends T> supplier) {

        return new String(factoryExpectedForNothing, UTF_8) + checkNotNull(data);
      }

      @Override
      public void tearDown() throws IOException {
        factory.tearDown();
      }
    };
  }

  public static ByteSourceFactory asSlicedByteSourceFactory(
      ByteSourceFactory factory, long off, long len) {
    checkNotNull(factory);
    return new ByteSourceFactory() {
      @Override

   */
  public void callAndAssertThrows(
      Class<? extends Throwable> expected, String methodName, Object... arguments)
      throws Exception {
    checkNotNull(expected);
    checkNotNull(methodName);
    checkNotNull(arguments);
    sendRequest(methodName, arguments);
    assertThat(getResponse(methodName).getThrowable()).isInstanceOf(expected);
  }

  /**

    return connections;
  }

  @Override
  @CanIgnoreReturnValue
  public @Nullable V putEdgeValue(N nodeU, N nodeV, V value) {
    checkNotNull(nodeU, "nodeU");
    checkNotNull(nodeV, "nodeV");
    checkNotNull(value, "value");

    if (!allowsSelfLoops()) {
      checkArgument(!nodeU.equals(nodeV), SELF_LOOPS_NOT_ALLOWED, nodeU);
    }

  SingletonImmutableBiMap(K key, V value) {
    super(singletonMap(checkNotNull(key), checkNotNull(value)));
    this.singleKey = key;
    this.singleValue = value;
  }

  private SingletonImmutableBiMap(K key, V value, SingletonImmutableBiMap<V, K> inverse) {
    super(singletonMap(checkNotNull(key), checkNotNull(value)));
    this.singleKey = key;
    this.singleValue = value;
    this.inverse = inverse;

    return connections;
  }

  @Override
  @CanIgnoreReturnValue
  public boolean addEdge(N nodeU, N nodeV, E edge) {
    checkNotNull(nodeU, "nodeU");
    checkNotNull(nodeV, "nodeV");
    checkNotNull(edge, "edge");

    if (containsEdge(edge)) {
      EndpointPair<N> existingIncidentNodes = incidentNodes(edge);

  @CanIgnoreReturnValue // TODO(kak): consider removing this
  @Override
  public <T> T newProxy(
      T target, Class<T> interfaceType, long timeoutDuration, TimeUnit timeoutUnit) {
    checkNotNull(target);
    checkNotNull(interfaceType);
    checkNotNull(timeoutUnit);
    return target; // ha ha
  }

  @CanIgnoreReturnValue // TODO(kak): consider removing this
  @Override
  @ParametricNullness