Help with Bind (not working)

I have this entity:

public class ProtocoloVo {
    Long numero;
    @JsonSerialize(using = LocalDateSerializer.class)
    @JsonDeserialize(using = LocalDateDeserializer.class)
    LocalDate date;

and create this binder in my class

TextField protocolo= new TextField("Nº do protocolo","Digite aqui o nº do protocolo");
    DatePicker dataProtocolo = new DatePicker("Data do protocolo");
private BeanValidationBinder<ProtocoloVo> binder = new BeanValidationBinder<>(ProtocoloVo.class);
private void bindCampos() {
        binder.forField(this.protocolo).withConverter(new StringToLongConverter(0l,"Erro")).withNullRepresentation(0l).bind(ProtocoloVo::getNumero, ProtocoloVo::setNumero);
        binder.forField(this.dataProtocolo).bind(ProtocoloVo::getDate, ProtocoloVo::setDate);
		binder.setBean(new ProtocoloVo());


So if I run this.binder.isValid() always return true, even if I don’t select an date in my field dataProtocolo, anyone kwno what I’m doing wrong?