onError method
Replaces the error event handler of this subscription.
The handleError function must be able to be called with either
one positional argument, or with two positional arguments
where the seconds is always a StackTrace.
The handleError argument may be null, in which case further
error events are considered unhandled, and will be reported to
Zone.handleUncaughtError.
The provided function is called for all error events from the stream subscription.
This method replaces the current handler set by the invocation of Stream.listen, by calling asFuture, or by a previous call to onError.
Implementation
@override
Never onError(Function? handleError) => _unsupportedError();