java negate boolean BiFunction

I have a class which will check if a key is/isn't included into a set of keys. This conditions are described in Map with use of MathingTypes

public enum MatchingType {
    MATCH, MISMATCH
}

Map with matching type predicates

Map<MatchingType, Function<Set<String>, Predicate<String>>> predicateMap =
        Map.of(
                MATCH, set -> set::contains,
                MISMATCH, set -> not(set::contains)
        );

An example of usage

public boolean isKeyAvailable(String key, MatchingType matchingType, Set<String> keys) {
    return predicateMap.get(matchingType)
                       .apply(keys)
                       .test(key);
}

Now I see that code from above is possible to refactor with the use of BiFunction.

Map<MatchingType, BiFunction<Set<String>, String, Boolean>> predicateMap =
        Map.of(
                MATCH, Set::contains,
                MISMATCH, Set::contains //how to negate?
        );

public boolean isKeyAvailable(String key, MatchingType matchingType, Set<String> keys) {
    return predicateMap.get(matchingType)
                       .apply(keys, key);
}

But how does it possible to negate Set::contains?

As of [tag:java-11] there is a static method Predicate.not(Predicate) however, there is not such method in BiPredicate.

You might want to use BiPredicate as is with its instance method negate, which is available since its release as of [tag:java-8]:

BiPredicate<Set<String>, String> biPredicate = Set::contains;
    
Map<MatchingType, BiPredicate<Set<String>, String>> biPredicateMap =
    Map.of(
        MatchingType.MATCH, biPredicate,
        MatchingType.MISMATCH, biPredicate.negate()
    );

boolean result = biPredicateMap.get(matchingType)
                               .test(keys, key);

The Function based functional interface don't have negation since their lambda expressions are not guaranteed to return Boolean.