Fix handling of missing Endpoint for client communication

The `getEndpointForClient()` threw an `InvalidStateException`if no Endpoint could be found for the Client. However, this exception had not been caught or otherwise been handled apropriately by any code yet. Thus I changed this to throw a `ResouceAccessException`instead which is properly handled.
IMO on private methods, avoid javadoc if it's just "@param request the request" that's not helping readability