Java: Add to Guava ImmutableList if optional value is present

Looking for an ideal way to add values optionally to list. Final list must be immutable.

Example-

Optional<Item> optionalItem = getOptionalItemFromSomewhereElse();

List<Item> list = ImmutableList.builder()
                      .add(item1) 
                      .add(item2)
                      .optionallyAdd(optionalItem)
                  .build();