in locales-common/src/main/java/com/spotify/i18n/locales/common/impl/LocaleAffinityCalculatorBaseImpl.java [183:191]
public final LocaleAffinityCalculator build() {
final LocaleAffinityCalculatorBaseImpl built = autoBuild();
for (ULocale locale : built.againstLocales()) {
Preconditions.checkState(
!isSameLocale(locale, ULocale.ROOT),
"The locales against which affinity needs to be calculated cannot contain the root.");
}
return built;
}