Getting WARNING level validation results with Binder in Vaadin 8

VaadinUI.java

package com.vaadin.example;

import com.vaadin.data.Binder;
import com.vaadin.data.ValidationResult;
import com.vaadin.server.VaadinRequest;
import com.vaadin.shared.ui.ErrorLevel;
import com.vaadin.ui.Notification;
import com.vaadin.ui.TextField;
import com.vaadin.ui.UI;

/**
 * @author Alejandro Duarte.
 */
public class VaadinUI extends UI {

    public static class Bean {

        private String value;

        public String getValue() {
            return value;
        }

        public void setValue(String value) {
            this.value = value;
        }

    }

    @Override
    protected void init(VaadinRequest vaadinRequest) {
        TextField textField = new TextField();

        Binder<Bean> binder = new Binder<>();
        binder.forField(textField)
                .withValidator((v, c) -> ValidationResult.create("This is a warning!", ErrorLevel.WARNING))
                .withValidator((v, c) -> ValidationResult.error("This is an error!"))
                .bind(Bean::getValue, Bean::setValue);

        binder.setBean(new Bean());

        binder.setValidationStatusHandler(statusChange ->
                statusChange.getFieldValidationStatuses().stream()
                        .map(r -> r.getValidationResults())
                        .flatMap(l -> l.stream())
                        .filter(r -> ErrorLevel.WARNING.equals(r.getErrorLevel().orElse(null)))
                        .forEach(w -> Notification.show(w.getErrorMessage()))
        );

        binder.validate();
    }

}