Apollo Federation - Entity field always returns object, not null

Question

I'm playing with Apollo Federation, and I'm using an entity from another service (File entity), in which this entity has the following resolver:

File: {
                    __resolveReference(reference, context) {
                        return null;
                    }
                },

Now, in spite of hard-coding / returning null from the resolver, I still get the object containing specified fields, which are all null.

This is the query I'm sending:

Is this normal behavior?

Thanks!