/**
* Map the identifier to all entities which match the given key. If the key did not match any
* entity then the key is added to {@link #unmapped()}
*
* @param key look up entities
* @param id the id
* @return an entity <i>handled</i> the identifier
* @see #unmapped()
*/
public boolean map(K key, Identifier id) {
if (id == null) throw new IllegalArgumentException("no identifier provided");
return map(key, annotations.getCrossReference(id));
}
