betaGroups property
The TestFlight groups this build is attached to, or null when the read did not ask.
Null and [] are different answers, and a consumer that treats them
alike reports the wrong one confidently. [] is Apple saying the build
is attached to no group; null is this package not having sent
include=betaGroups, which every read before schema 2 did. The second
renders as no external testers have this — true most of the time, which
is exactly why it goes unnoticed when it is not.
Internal and external groups are both here and are told apart by BetaGroupEntry.kind, never by counting or by name.
A lower bound rather than the list when unresolvedBetaGroups is not
zero. Every group here is one Apple named and sent; read that field
before treating [] as attached to nothing.
Implementation
final List<BetaGroupEntry>? betaGroups;