// Query Operations

  /**
   * Returns the number of occurrences of {@code element} in this multiset.
   *
   * @param element the element to look for
   * @return the nonnegative number of occurrences of the element
   */
  @Override
  public int count(@CheckForNull Object element) {
    AtomicInteger existingCounter = Maps.safeGet(countMap, element);
    return (existingCounter == null) ? 0 : existingCounter.get();
  }

                for (PluginExecution element : tgt) {
                    Object key = getPluginExecutionKey().apply(element);
                    merged.put(key, element);
                }

                for (PluginExecution element : src) {
                    Object key = getPluginExecutionKey().apply(element);
                    PluginExecution existing = merged.get(key);

      return unfiltered.add(element, occurrences);
    }

    @Override
    public int remove(@CheckForNull Object element, int occurrences) {
      checkNonnegative(occurrences, "occurrences");
      if (occurrences == 0) {
        return count(element);
      } else {
        return contains(element) ? unfiltered.remove(element, occurrences) : 0;
      }

     */
    @CanIgnoreReturnValue
    public Builder<E> addCopies(E element, int occurrences) {
      contents.add(checkNotNull(element), occurrences);
      return this;
    }

    /**
     * Adds or removes the necessary occurrences of an element such that the element attains the
     * desired count.
     *
     * @param element the element to add or remove occurrences of

  final transient E element;

  SingletonImmutableSet(E element) {
    this.element = Preconditions.checkNotNull(element);
  }

  @Override
  public int size() {
    return 1;
  }

  @Override
  public boolean contains(@CheckForNull Object target) {
    return element.equals(target);
  }

  @Override
  public UnmodifiableIterator<E> iterator() {

    /**
     * Return the index of the next lower element in the list, or {@code -1} if there is no such
     * element.
     */
    NEXT_LOWER {
      @Override
      int resultIndex(int higherIndex) {
        return higherIndex - 1;
      }
    },
    /**
     * Return the index of the next higher element in the list, or {@code list.size()} if there is
     * no such element.
     */
    NEXT_HIGHER {

      Iterable<? extends @Nullable Object> iterable, @CheckForNull Object element) {
    if (iterable instanceof Collection) {
      Collection<?> collection = (Collection<?>) iterable;
      return Collections2.safeContains(collection, element);
    }
    return Iterators.contains(iterable.iterator(), element);
  }

  /**
   * Removes, from an iterable, every element that belongs to the provided collection.
   *

   * #add(Object, int) add}{@code (element, 1)} instead.
   *
   * @param element the element to add one occurrence of; may be null only if explicitly allowed by
   *     the implementation
   * @return {@code true} always, since this call is required to modify the multiset, unlike other
   *     {@link Collection} types

            return mapping[fir]?.getOrNull()
        }

        override fun visitElement(element: FirElement) {
            withElement(element) {
                if (element in statements) {
                    // The leaf is in mapping, but its value is still 'null'
                    mapping.computeIfAbsent(element) { _ ->
                        unmappedCount -= 1

    int expectedHashCode = 0;
    for (E element : elements) {
      expectedHashCode += ((element == null) ? 0 : element.hashCode());
    }

    elements.add(null);
    collection = getSubjectGenerator().create(elements.toArray());
    assertEquals(
        "A Set's hashCode() should be the sum of those of its elements (with "
            + "a null element counting as having a hash of zero).",
        expectedHashCode,