public void addFieldRankFilterThreshold(String field, double filterThreshold) {
        verifyThat(!fieldsRankFilterThreshold.containsKey(field), "already has rank filter-threshold for field", field);
        verifyThat(filterThreshold >= 0.0 && filterThreshold <= 1.0, "must be a value in range [0, 1]", field);
        fieldsRankFilterThreshold.put(field, filterThreshold);
    }
This class holds the extracted information after parsing a
rank-profile block in a schema (.sd) file, using simple data
structures as far as possible.  Do not put advanced logic here!

@author arnej27959
config-model/src/main/java/com/yahoo/schema/parser/ParsedRankProfile.java