fail method
Implementation
void fail(Object error, [StackTrace? stackTrace]) {
if (completed) throw StateError('Request already completed.');
_remove();
_result.completeError(error, stackTrace);
}
void fail(Object error, [StackTrace? stackTrace]) {
if (completed) throw StateError('Request already completed.');
_remove();
_result.completeError(error, stackTrace);
}