code: function callsBackWithError(cb) {
    setTimeout(
        function () { 
          try {
            console.log('bad culprit', culprit); 
            cb(null, 'yay');
          } catch(err) {
            cb(err);
          }
        }
      , 20);
  }
docs: /*
  Demonstrates the correct way of handling errors in nodejs in general and thus also with runnel.
  E.g., catch them and invoke the callback with the caught error.
  This allows runnel to react properly, stop the call chain and call back the
  last function in the chain with the error.