I started writing my check for IsLowercase() before the hint about islower(), and ended up going a different route. Seems to work, or at least it doesn’t mind spaces, and \0.
bool FBullCowGame::IsLowerCase(FString Word) const
{
for (auto Letter : Word)
{
if (tolower(Letter) != Letter) {
return false;
}
}
return true;
}