Swagger OpenApi sends empty value "" instead of null and this ends up giving a 400 Bad Request status - spring-boot

Question

I'm doing a rest api in spring boot and I need to receive 3 normal values and a file, as you can see in the image below.
endpoint image in swagger
My problem is that it is not mandatory to send the file, so when I make the request without the file, instead of going null it goes "" which is considered a string and this ends up giving status 400, because it is waiting for a type MultipartFile.
My method in spring boot:
#Operation(tags = {"Contato"}, summary = "Atualizar contato", description = "Atualiza os dados de um contato ativo a partir do ID.")
#PutMapping(path = "/atualizarContato",consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
public ResponseDto atualizarContato(#ModelAttribute ContatoUpdateDto contatoDto) throws IOException {// fazer a logica}
My class, I even tried to put the default value in #Schema but it doesn't work.
package app.api.denuncia.Dto;
import org.springframework.web.multipart.MultipartFile;
import io.swagger.v3.oas.annotations.media.Schema;
public class ContatoUpdateDto {
#Schema(description = "O identificador (ID) do contato", required = true)
private int id;
#Schema(description = "O nome do contato", required = true)
private String nome;
#Schema(description = "O número de telefone do contato")
private String telefone;
#Schema(description = "Imagem que representa o contato")
private MultipartFile logotipo;
public ContatoUpdateDto() {
}
public String getTelefone() {
return telefone;
}
public void setTelefone(String telefone) {
this.telefone = telefone;
}
public String getNome() {
return nome;
}
public void setNome(String nome) {
this.nome = nome;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public MultipartFile getLogotipo() {
return logotipo;
}
public void setLogotipo(MultipartFile logotipo) {
this.logotipo = logotipo;
}
}
I just need that instead of sending "" it sends null.
The error:
image 1
image 2