* {@code LoginModule} or {@code null}.
*/
@CheckForNull
protected Whiteboard getWhiteboard() {
if (whiteboard == null && callbackHandler != null) {
WhiteboardCallback cb = new WhiteboardCallback();
try {
callbackHandler.handle(new Callback[]{cb});
whiteboard = cb.getWhiteboard();
} catch (Exception e) {
log.debug("Unable to retrieve the Whiteboard via callback", e);
}
}
return whiteboard;