Cannot query "collection & Product.facetValues" at the same time

[chladog]

Describe the bug
When trying to query collection by id or slug and retrieving {{collectionData}}.productVariants.product.facetValues.{{value}} we get error "Cannot return null for non-nullable field Product.facetValues."

To Reproduce
Steps to reproduce the behavior:
https://demo.vendure.io/shop-api and run query:
query { collection(slug: "electronics") { productVariants { items { product { facetValues { name code } } } } } }
Expected behavior
We are able to query data with facetValues included.

Environment:
I encountered this problem with Postgres DB, dunno if bug occurs with other DB...