public SortedSet<Reference> queryFeaturesNotDeclared() {
        return Collections.unmodifiableSortedSet(queryFeaturesNotDeclared);
    }
Returns an unmodifiable view of the query features which was requested but for which we have no type info
(such that they default to TensorType.empty), shared between all instances of this
involved in resolving a particular rank profile.
config-model/src/main/java/com/yahoo/schema/MapEvaluationTypeContext.java