Class Car 
{
    /**
    * @var string
    */
    private string $brandName;

   public function getBrandName(): string
    {
        return $this->brandName;
    }

    public function setBrandName(string $brandName): self
    {
        $this->brandName = $brandName;

        return $this;
    }
}

Class CarType extends AbstractType 
{
    /**
     * {@inheritDoc}
     */
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('brandName')
        ;
    }

    /**
     * {@inheritDoc}
     */
    public function configureOptions(OptionsResolver $resolver)
    {
        $resolver->setDefaults([
            'data_class' => Car::class,
        ]);
    }
}

Class CarController extends AbstractController
{
    public function postCar(Request $request, FormFactoryInterface $formFactory): Response
    {
        $form = $formFactory->create(CarType::class);
        $form->handleRequest($request); // this will throw the error
    }
}