In `maybe`, would it make sense to check the args passed to the wrapper against the number of args the original function expects? Something like this:

    function maybe (fn) {
      var expected_number_of_args = fn.length;
      return function () {
        var i, arg;
        for (i = 0; i < expected_number_of_args; ++i) {
          arg = arguments[i];
          if (arg === null || typeof arg === 'undefined') {
            return null;
          }
        }
        return fn.apply(this, arguments)
      }
    }