Nested read always returns null for "snapshot.data.data()"?

[sabetAI]

If I perform a nested read that is deeper than 2 levels ie FirebaseFirestore.instance.doc(a/b/c).get(), the snapshot.data.data() field always returns null (when snap.hasData). For efficiency reasons, I'd like to perform partial reads (ie field c of document b), is this possible or can I only retrieve the whole document as a snapshot?