As you can see here: http://cal10n.qos.ch/xref/ch/qos/cal10n/IMessageConveyor.html#58
The interface mandates all implementors to optionally throw this exception. This design has tow flaws:

1. This exception is not documented in the JavaDocs
2. It extends the RuntimeException (unchecked exception), which indicates an unrecoverable state of the client.

Such exceptions should never be declared in the throws block since the client can't do anything about it.
See reference here: http://www.javapractices.com/topic/TopicAction.do?Id=129
and Joshua Bloch's great book: http://www.amazon.de/Effective-Java-Programming-Language-Guide/dp/0321356683/ref=sr_1_1?ie=UTF8&s=books-intl-de&qid=1285356616&sr=8-1-spell