async.waterfall gotchas

waterfall.js

var async = require('async');
/*jshint noarg:false */

function first(next) {
  console.log('first', arguments);
  next(); // no params = nothing in next step
}

function second(next) {
  console.log('second', arguments);
  next(null); // no "result" params = nothing in next step
}

function third(next) {
  console.log('third', arguments);
  next(null,null); // explicit null param = one parameter in next step
}

function fourth(isNull, next) {
  console.log('fourth', arguments);
  next(null,'all done');
}

async.waterfall([
  first,
  second,
  third,
  fourth
], function(err,lastResult) {
  console.log('finally', arguments);
});