try {
        in.close();
      } finally {
        in = null;
      }
    }
  }

  /** Closes the current input stream and opens the next one, if any. */
  private void advance() throws IOException {
    close();
    if (it.hasNext()) {
      in = it.next().openStream();
    }
  }

  @Override
  public int available() throws IOException {
    if (in == null) {
      return 0;
    }

    Iterator<String> keyIterator = keys.iterator();
    keyIterator.next();
    keyIterator.remove();
    assertFalse(underlying.containsKey("c"));

    Collection<String> values = map.values();
    values.remove("4");
    assertFalse(underlying.containsKey("d"));

    Iterator<String> valueIterator = values.iterator();
    valueIterator.next();
    valueIterator.remove();
    assertFalse(underlying.containsKey("e"));

    Iterator<Entry<K, Collection<V>>> entryIterator = unfiltered.asMap().entrySet().iterator();
    boolean changed = false;
    while (entryIterator.hasNext()) {
      Entry<K, Collection<V>> entry = entryIterator.next();
      K key = entry.getKey();
      Collection<V> collection = filterCollection(entry.getValue(), new ValuePredicate(key));
      if (!collection.isEmpty()

    Entry<String, Collection<Integer>> entry = iterator.next();
    assertEquals(null, entry.getKey());
    assertThat(entry.getValue()).containsExactly(7, 3, 1);
    entry = iterator.next();
    assertEquals("tree", entry.getKey());
    assertThat(entry.getValue()).containsExactly(null, 0);
    entry = iterator.next();
    assertEquals("google", entry.getKey());

  }

  private Entry<K, V> getEntryNullReplaces() {
    Iterator<Entry<K, V>> entries = getSampleElements().iterator();
    for (int i = 0; i < getNullLocation(); i++) {
      entries.next();
    }
    return entries.next();
  }

  /**
   * @return an array of the proper size with {@code null} as the value of the middle element.
   */
  protected Entry<K, V>[] createArrayWithNullValue() {

    multiset.add(multiset, 2);
    Multiset<Multiset<?>> copy = SerializableTester.reserialize(multiset);
    assertEquals(2, copy.size());
    assertSame(copy, copy.iterator().next());
  }

  @J2ktIncompatible
  @GwtIncompatible // Only used by @GwtIncompatible code
  private static class MultisetHolder implements Serializable {
    private final Multiset<?> member;

                return true;
            }
        }
        return false;
    }

    @Override
    public E next() {
        if (!hasNext()) {
            throw new NoSuchElementException();
        }
        return iterators[index].next();
    }

    @Override
    public void remove() {
        throw new ClUnsupportedOperationException("remove");
    }

    checkNotNull(appendable);
    if (parts.hasNext()) {
      appendable.append(toString(parts.next()));
      while (parts.hasNext()) {
        appendable.append(separator);
        appendable.append(toString(parts.next()));
      }
    }
    return appendable;
  }

  /**

   */
  protected @Nullable Entry<E> standardFirstEntry() {
    Iterator<Entry<E>> entryIterator = entrySet().iterator();
    if (!entryIterator.hasNext()) {
      return null;
    }
    Entry<E> entry = entryIterator.next();
    return Multisets.immutableEntry(entry.getElement(), entry.getCount());
  }

  @Override
  public @Nullable Entry<E> lastEntry() {
    return delegate().lastEntry();
  }

  /**

): List<T> {
  val ia = a.iterator()
  val ib = b.iterator()

  return buildList {
    while (ia.hasNext() || ib.hasNext()) {
      if (ia.hasNext()) {
        add(ia.next())
      }
      if (ib.hasNext()) {
        add(ib.next())
      }
    }
  }