'Check if a key has been set to a value and not inheriting from its default.'

def isset(self, key):

    opt = self.lookup_key(key)
    if (not (opt.flags & FLAG_NOSTORE)):
        result = self.store.get(opt, silent=True)
        if (result is not None):
            return True
    return (key in settings.SENTRY_OPTIONS)
