Spring Boot 2.0.0M2 Thymeleaf 3 failed to convert field - spring

Question

After upgrading to spring-boot-2-m2 (thymeleaf 3) I am getting failed conversion errors for fields that correspond to JPA relationships.
Failed to convert from type [#javax.persistence.ManyToOne #javax.persistence.JoinColumn com.pps2....entities.FormType] to type [java.lang.String] for value 'com.pps2.....FormType#819841af'; nested exception is org.springframework.core.convert.ConverterNotFoundException: No converter found capable of converting from type [java.util.Optional<?>] to type [java.lang.String]
JPA Entity
#ManyToOne(fetch = FetchType.EAGER)
#JoinColumn(name = "id_form_type")
private FormType type;
public FormType getType() {
return type;
}
The code in the template is:
<select th:field="*{type}" class="col-xs-12">
Throws similar failed conversion error.
Of course when putting direct reference it works, but in that case it breaks a lot of templates in the project. And generates name as type.id and not type.
Working example
<select th:field="*{type.id}" class="col-xs-12">
Question - Why did they change the API? And is there a way to resolve it without rechecking all the templates (e.g. writing converter?)?

Answer 1

The solution is to write your own Optional<T> to String converter. I do not know why it was excluded from Spring Boot 2 M2
Converter code
import org.springframework.core.convert.converter.Converter;
import org.springframework.stereotype.Component;
import java.util.Objects;
import java.util.Optional;
#Component
final class OptionalToString implements Converter<Optional<?>, String> {
public String convert(Optional<?> source) {
return Objects.toString(source.get(),"");
}
}
Another option
Is to specify directly the column (like id)
Working example <select th:field="*{type.id}" class="col-xs-12">