* and values are the result of applying the provided mapping functions to the input elements.
   *
   * <p>If the mapped keys contain duplicates (according to {@link Object#equals(Object)}), the
   * values are merged using the specified merging function. If the merging function returns {@code
   * null}, then the collector removes the value that has been computed for the key thus far (though
   * future occurrences of the key would reinsert it).

    if (iterable instanceof Collection) {
      return ((Collection<?>) iterable).isEmpty();
    }
    return !iterable.iterator().hasNext();
  }

  /**
   * Returns an iterable over the merged contents of all given {@code iterables}. Equivalent entries
   * will not be de-duplicated.
   *
   * <p>Callers must ensure that the source {@code iterables} are in non-descending order as this

  public static <T extends @Nullable Object> PeekingIterator<T> peekingIterator(
      PeekingIterator<T> iterator) {
    return checkNotNull(iterator);
  }

  /**
   * Returns an iterator over the merged contents of all given {@code iterators}, traversing every
   * element of the input iterators. Equivalent entries will not be de-duplicated.
   *

    assertFalse("heap contains larry which has been removed", mmHeap.contains("larry"));
    assertTrue("heap does not contain sergey", mmHeap.contains("sergey"));
    assertTrue("Could not remove larry", mmHeap.removeAll(Lists.newArrayList("sergey", "eric")));
    assertFalse("Could remove nikesh which is not in the heap", mmHeap.remove("nikesh"));
    assertEquals(4, mmHeap.size());
  }

  public void testCreateWithOrdering() {

    }
    try {
      unmod.compute(4, (k, v) -> v);
      fail("UnsupportedOperationException expected");
    } catch (UnsupportedOperationException expected) {
    }
    try {
      unmod.merge(4, "four", (k, v) -> v);
      fail("UnsupportedOperationException expected");
    } catch (UnsupportedOperationException expected) {
    }
    try {
      unmod.clear();

                    entryKey, hash, value, valueReference.getWeight(), RemovalCause.COLLECTED);
              } else if (map.isExpired(e, now)) {
                // This is a duplicate check, as preWriteCleanup already purged expired
                // entries, but let's accommodate an incorrect expiration queue.
                enqueueNotification(
                    entryKey, hash, value, valueReference.getWeight(), RemovalCause.EXPIRED);

            immutableCell("two", "dos", 2),
            immutableCell("three", "tres", 3));
  }

  public void testToTableNullMerge() {
    // TODO github.com/google/guava/issues/6824 - the null merge feature is not compatible with the
    // current nullness annotation of the mergeFunction parameter. Work around with casts.
    BinaryOperator<@Nullable Integer> mergeFunction = (v1, v2) -> null;

      this.mergeFunction = mergeFunction;
    }

    void put(K key, V value) {
      if (map == null) {
        map = new EnumMap<>(singletonMap(key, value));
      } else {
        map.merge(key, value, mergeFunction);
      }
    }

    EnumMapAccumulator<K, V> combine(EnumMapAccumulator<K, V> other) {
      if (this.map == null) {
        return other;
      } else if (other.map == null) {

   * iterate over keys in their enum definition order, not encounter order.
   *
   * <p>If the mapped keys contain duplicates, the values are merged using the specified merging
   * function.
   *
   * @since 33.2.0 (available since 21.0 in guava-jre)
   */
  @SuppressWarnings({"AndroidJdkLibsChecker", "Java7ApiChecker"})

      this.mergeFunction = mergeFunction;
    }

    void put(K key, V value) {
      if (map == null) {
        map = new EnumMap<>(singletonMap(key, value));
      } else {
        map.merge(key, value, mergeFunction);
      }
    }

    EnumMapAccumulator<K, V> combine(EnumMapAccumulator<K, V> other) {
      if (this.map == null) {
        return other;
      } else if (other.map == null) {