isBot method
Whether userAgent belongs to a known crawler.
null or empty User-Agents count as regular users, so real visitors
never accidentally get the bot response.
Implementation
bool isBot(String? userAgent) {
if (userAgent == null || userAgent.isEmpty) return false;
final ua = userAgent.toLowerCase();
final override = _override;
if (override != null) return override.any(ua.contains);
return _defaultMatcher.hasMatch(ua) ||
_extra.any((pattern) => ua.contains(pattern.toLowerCase()));
}