@Override
    protected String appendAttributeToQuery(final String queryBuilder, final String dataAttribute, final List<Object> queryValues) {
        if (queryBuilder != null) {
            return queryBuilder;
        }
        val keyAttributeName = this.queryAttributeName != null
            ? this.queryAttributeName
            : getUsernameAttributeProvider().getUsernameAttribute();
        if (keyAttributeName.equals(dataAttribute)) {
            return String.valueOf(queryValues.getFirst());
        }
        return null;
    }
Sets backing map.

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