if ((handler != null) && (assign == null)) {
final Scheduler scheduler = this.scheduler.get ();
Preconditions.checkState (scheduler != null);
this.reactor.transcript.traceDebugging ("invocking unregister callback on handler `%{object}` for proxy `%{object:identity}` (owned by actor `%{object:identity}`) backed by isolate `%{object:identity}` (owned by scheduler `%{object:identity}`)...", handler, this.proxy, this, scheduler.isolate, scheduler);
try {
handler.unregisteredCallbacks (this.specification.cast (this.proxy));
} catch (final Throwable exception) {
this.reactor.exceptions.traceDeferredException (exception);
this.triggerFailure (exception);
return;
}