Dart sound null safety is currently in beta, however; some FlutterFire packages have preview versions of null-safety implementations that are available to use.
The below table outlines the latest null-safe plugin versions:
Using with other non-null-safe FlutterFire packages
Mixing currently published null-safety FlutterFire packages alongside published non-nullsafety packages is not supported.
Not all FlutterFire packages have null-safety versions available yet. If you need to use the null-safe packages alongside the non-null-safe packages then it's recommended you switch to sourcing your FlutterFire packages directly from the main FlutterFire repository (rather than pub.dev) where the packages have compatible version constraints.
To provide feedback on these versions or to see progress updates: see this GitHub discussion.