How can I access product data from line_item using CartJS?

[abater]

I'm using CartJS and the rivets library to render my cart. It's all good, except I need the product property on each `line_item`, but it seems to be undefined, despite the Shopify docs stating that the `line_item` object should have an associated `product`. Is there a way to access that data?

To be specific, what I'm trying to do is access an additional piece of data on each product that has been stored as a metafield.