@SuppressWarnings("OptionalUsedAsFieldOrParameterType")
  default R isNot(Optional<Boolean> optional) {
    Objects.requireNonNull(optional, "optional");
    return optional.map(this::isNot).orElseGet(this::isPresent);
  }
Do not match current optional boolean attribute. For empty
optional matching is equivalent to {@link #isPresent()} (not absent), otherwise standard
{@link #isNot(boolean)} (boolean)} matching is used.

@param optional optional boolean to match with
@throws NullPointerException if argument is null
criteria/common/src/org/immutables/criteria/matcher/OptionalBooleanMatcher.java