public CallbackCompletion<Void> close(final TExtra extra) {
this.transcript.traceDebugging("Closing file with extra `%{object}`" , extra);
final CallbackCompletion<Void> completion = this.file.close();
if(this.callback != null) {
completion.observe(new CallbackCompletionObserver() {
@Override
public CallbackCompletion<Void> completed(CallbackCompletion<?> completion_) {
assert (completion == completion_);