public OptionalDouble getFilterThreshold() {
        if (filterThreshold != null) {
            return OptionalDouble.of(filterThreshold);
        }
        return uniquelyInherited(RankProfile::getFilterThreshold, OptionalDouble::isPresent, "filter-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