Docs and error message for this function are out of date. Also I think the boolean handling in that if statement can be a little more readable:

```javascript
var isRouteValid = (_.isString(route) || _.isRegExp(route));
var isHandleValid = (_.isFunction(handler) || _.isArray(handler));
if (_.isString(method) && isRouteValid && isHandlerValid) {
  ...
}
```