* Returns the message from the given extension.
* @param extension the given extension.
* @return the message from the given extension, or {@code null} if the extension is not referring to a message.
*/
public Message messageFrom(TypeExtension extension) {
ExtensibleTypeLink link = extension.getType();
if (link == null) {
return null;
}
ExtensibleType type = link.getTarget();
return (type instanceof Message) ? (Message) type : null;
}