How to call FieldValue.arrayUnion()

[JordanTYC]

Hello,

I use this package, all is fine when I do this.firebase.firestore.(+something) in my service.

I would like to add a value in an array (from Firestore) via FieldValue.arrayUnion() but I am unable to retrieve FieldValue.
I tried FirebaseFirestore.FieldValue.arrayUnion(), but FirebaseFirestore is not defined.

I would greatly appreciate your assistance.