userFraction property
Play's userFraction, exactly as sent.
Play omits it exactly when it means one. Google sets it only for
inProgress and halted, so a completed rollout carries no fraction at
all, and reading this field alone answers null for the release that
reached everybody. That is what PlayReleaseStatus.audienceFraction is
for, and where Google's documented 0 < fraction < 1 is cited and
caveated — nothing here has measured it against a live account.
Implementation
final double? userFraction;