Fatal error and deprecated code: StateFieldBuilder

saidatom → changed the visibility of the branch 3542871-fatal-error-and to hidden.

The change isn't valid as is.
The deprecation helper was introduced in D10.1.3, and we currently still support D9. So either we drop support as part of this change, or we do this differently.

Also the return type issue can be fixed separately from the renderInIsolation() calls.