presto-spi/src/main/java/io/prestosql/spi/predicate/TupleDomain.java/TupleDomain/extractFixedValues
class TupleDomain:    public static <T> Optional<Map<T, NullableValue>> extractFixedValues(TupleDomain<T> tupleDomain)
    {
        if (!tupleDomain.getDomains().isPresent()) {
            return Optional.empty();
        }

        return Optional.of(tupleDomain.getDomains().get()
                .entrySet().stream()
                .filter(entry -> entry.getValue().isNullableSingleValue())
                .collect(toLinkedMap(Map.Entry::getKey, entry -> new NullableValue(entry.getValue().getType(), entry.getValue().getNullableSingleValue()))));
    }