* comparator (which might be the keys' natural order), are not allowed, and will cause {@link
     * #build} to fail.
     */
    @CanIgnoreReturnValue
    @Override
    public Builder<K, V> put(K key, V value) {
      ensureCapacity(size + 1);
      checkEntryNotNull(key, value);
      keys[size] = key;
      values[size] = value;
      size++;