return get(key).add(value);
  }

  @CanIgnoreReturnValue
  @Override
  public boolean putAll(@ParametricNullness K key, Iterable<? extends V> values) {
    checkNotNull(values);
    // make sure we only call values.iterator() once
    // and we only call get(key) if values is nonempty
    if (values instanceof Collection) {
      Collection<? extends V> valueCollection = (Collection<? extends V>) values;

    return get(key).add(value);
  }

  @CanIgnoreReturnValue
  @Override
  public boolean putAll(@ParametricNullness K key, Iterable<? extends V> values) {
    checkNotNull(values);
    // make sure we only call values.iterator() once
    // and we only call get(key) if values is nonempty
    if (values instanceof Collection) {
      Collection<? extends V> valueCollection = (Collection<? extends V>) values;