heroFallback function
The deterministic last-resort theme for (seed, family) when every
generator attempt fails: one of the family's heroes (or any hero).
Implementation
ThemeSpec heroFallback(
int seed,
ThemeFamily family, {
bool accessible = false,
}) {
var pool = heroesFor(family);
if (pool.isEmpty) pool = heroThemes;
final hero = pool[(seed & 0xFFFFFFFF) % pool.length];
return heroForAccessible(hero, accessible: accessible);
}