anchor.diff:  
     if ((response as dynamic) == null) {
       // Handle nulls flowing from opt-out code
  -    await _writeResponse(_logError(shelfRequest, 'null response from handler.'),
  +    await _writeResponse(
  +        _logError(
  +            shelfRequest, 'null response from handler.', StackTrace.current),
           request.response);
       return;
     }
  
positive.code: 
  // TODO(kevmoo) A developer mode is needed to include error info in response
  // TODO(kevmoo) Make error output plugable. stderr, logging, etc
  Response _logError(Request request, String message, [StackTrace? stackTrace]) {
    // Add information about the request itself.
    var buffer = StringBuffer();
    buffer.write('${request.method} ${request.requestedUri.path}');
  
negative.code:   return Response.internalServerError();
  }
  
  void _logTopLevelError(String message, StackTrace stackTrace) {
    final chain = Chain.forTrace(stackTrace)
        .foldFrames((frame) => frame.isCore || frame.package == 'shelf')
        .terse;
  
  