Given the following NestJS JWT guard code snippet, what will happen if the request has no Authorization header?

Given the following NestJS JWT guard code snippet, what will happen if the request has no Authorization header?

canActivate(context: ExecutionContext) {
  const request = context.switchToHttp().getRequest();
  const authHeader = request.headers['authorization'];
  if (!authHeader) {
    throw new UnauthorizedException('No token provided');
  }
  // further token validation...
  return true;
}