docs: function expandErrors(logger) {
      var oldLogFunc = logger.log
      logger.log = function() {
        var args = Array.prototype.slice.call(arguments, 0)
        if (args.length >= 2 && args[1] instanceof Error) {
          args[1] = args[1].stack
        }
        return oldLogFunc.apply(this, args)
      };
      return logger
    }