Builder(int initialCapacity) {
      this.alternatingKeysAndValues = new @Nullable Object[2 * initialCapacity];
      this.size = 0;
      this.entriesUsed = false;
    }

    private void ensureCapacity(int minCapacity) {
      if (minCapacity * 2 > alternatingKeysAndValues.length) {
        alternatingKeysAndValues =
            Arrays.copyOf(
                alternatingKeysAndValues,

          contents.ensureCapacity(Math.max(contents.size(), backingMap.size()));
          for (int i = backingMap.firstIndex(); i >= 0; i = backingMap.nextIndex(i)) {
            addCopies(backingMap.getKey(i), backingMap.getValue(i));
          }
        } else {
          Set<? extends Entry<? extends E>> entries = multiset.entrySet();

      this.comparator = checkNotNull(comparator);
      this.keys = new @Nullable Object[initialCapacity];
      this.values = new @Nullable Object[initialCapacity];
    }

    private void ensureCapacity(int minCapacity) {
      if (minCapacity > keys.length) {
        int newCapacity = ImmutableCollection.Builder.expandedCapacity(keys.length, minCapacity);
        this.keys = Arrays.copyOf(keys, newCapacity);