@Override
    public Set<String> mergeAvailableQueryAttributes(final Set<String> toModify, final Set<String> toConsider) {
        toModify.addAll(toConsider);
        return toModify;
    }
Merges the Sets of Persons additively calling the abstract {@link #mergePersonAttributes(Map, Map)} method on the
attributes of Persons that exist in both sets. The {@link #mergeAvailableQueryAttributes(Set, Set)} and {@link #mergePossibleUserAttributeNames(Set, Set)}
methods do a simple additive merge of the sets. These can be overridden by subclasses.

@author Eric Dalquist
@since 7.1.0
core/cas-server-core-authentication-api/src/main/java/org/apereo/cas/authentication/principal/merger/BaseAdditiveAttributeMerger.java