Cannot add lists of filterable items as objects

[David Leonardi]

When defining a new filterable property on a model, it would be fantastic if the value could be a list of items, instead of just a fixed value.

For instance, i'd like to have something like:

users / groups => group1... group10

i can filter a given group by user, and find a given user's groups.

In the current implementation, I'm trying to do this by passing an object to a updateById(id, {groups: group1: true}) but that breaks in the getPathString method.