for (Entry<?, ?> entry : enumMap.entrySet()) {
        checkNotNull(entry.getKey());
        checkNotNull(entry.getValue());
      }
      @SuppressWarnings({"unchecked", "rawtypes"})
      // immutable collections are safe for covariant casts
      // and getting the generics right for EnumMap is difficult to impossible
      ImmutableMap<K, V> result = ImmutableEnumMap.asImmutable(new EnumMap(enumMap));

     * ImmutableMap#builder}.
     */
    public Builder() {
      this(ImmutableCollection.Builder.DEFAULT_INITIAL_CAPACITY);
    }

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

     * ImmutableMap#builder}.
     */
    public Builder() {
      this(ImmutableCollection.Builder.DEFAULT_INITIAL_CAPACITY);
    }

    @SuppressWarnings({"unchecked", "rawtypes"})
    Builder(int initialCapacity) {
      this.entries = new @Nullable Entry[initialCapacity];
      this.size = 0;
      this.entriesUsed = false;
    }

    private void ensureCapacity(int minCapacity) {