@Override
    public Set<String> getPossibleUserAttributeNames(final PersonAttributeDaoFilter filter) {
        return Set.copyOf(this.possibleUserAttributeNames);
    }
Sets backing map.

@param backingMap the backing map
support/cas-server-support-person-directory-core/src/main/java/org/apereo/cas/persondir/MappablePersonAttributeDao.java