public void setRankProperty(String name, String parameter) {
        var old = rankProperties.get(name);
        if (old != null) {
            if (old.size() != 1) {
                throw new IllegalStateException("setRankProperty used for multi-valued property " + name);
            }
            var oldVal = old.get(0).getValue();
            if (! oldVal.equals(parameter)) {
                throw new IllegalArgumentException("setRankProperty would change property " + name + " from " + oldVal + " to " + parameter);
            }
        } else {
            addRankProperty(new RankProperty(name, parameter));
        }
    }
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