Array of parameters in Restangular

I'm trying to pass some filters to my getList method of Restangular.

In my app I have this:

var filters = Filters.get();

var query = {};
for (var i in filters) {
  query['filters['+i+']'] = filters[i];
}
query['userId'] = userId;

Restangular.all('pets').getList(query).then(...

And in the server side (Node + ExpressJS) I have this:

var filters = req.query.filters;
for(var i in filters){
  console.log(filters[i]);
}

that is consoling objects like this:

{"category":"Tipo","options":[{"name":"Perros","realName":"perro","checked":true},{"name":"Gatos","realName":"gato","checked":true}]} 

But, I don't know why when I try console.log(filters[i].category); is not consoling Tipo

Can anyone see something that I am not seeing, or has a better way to do this?

Thanks!