anchor.diff:  
   // 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]) {
  +Response _logError(Request request, String message, StackTrace stackTrace) {
     // Add information about the request itself.
     var buffer = StringBuffer();
     buffer.write('${request.method} ${request.requestedUri.path}');
  
positive.code:   return Response.internalServerError();
  }
  
  void _logTopLevelError(String message, [StackTrace? stackTrace]) {
    var chain = Chain.current();
    if (stackTrace != null) {
      chain = Chain.forTrace(stackTrace);
    }
    chain = chain
        .foldFrames((frame) => frame.isCore || frame.package == 'shelf')
        .terse;
  
  
negative.code: 
    if ((response as dynamic) == null) {
      // Handle nulls flowing from opt-out code
      await _writeResponse(
          _logError(
              shelfRequest, 'null response from handler.', StackTrace.current),
          request.response);
      return;
    }
  