public OptionalDouble getApproximateThreshold() {
        if (approximateThreshold != null) {
            return OptionalDouble.of(approximateThreshold);
        }
        return uniquelyInherited(RankProfile::getApproximateThreshold, OptionalDouble::isPresent, "approximate-threshold").orElse(OptionalDouble.empty());
    }
Returns a read only map view of the rank properties to use in this profile. This is never null.
config-model/src/main/java/com/yahoo/schema/RankProfile.java