Vaadin 10 code showing an issue with required TextField https://github.com/vaadin/vaadin-text-field-flow/issues/82

MainView.java

package eu.przepiora.mac;

import com.vaadin.flow.component.dependency.HtmlImport;
import com.vaadin.flow.component.orderedlayout.VerticalLayout;
import com.vaadin.flow.component.textfield.TextField;
import com.vaadin.flow.data.binder.Binder;
import com.vaadin.flow.router.Route;

@HtmlImport("styles/shared-styles.html")
@Route("")
public class MainView extends VerticalLayout {

    public MainView() {
        Binder<PersonBean> binder = new Binder<>(PersonBean.class);
        PersonBean joeDeveloper = new PersonBean();
        joeDeveloper.setFirstName("Joe");
        joeDeveloper.setLastName("Developer");

        binder.setBean(joeDeveloper);

        TextField firstName = new TextField();
        TextField lastName = new TextField();

        binder.forField(firstName)
                .withValidator(s -> s.equals("Joe"), "Must be Joe")
                .asRequired()
                .bind("firstName");
        binder.forField(lastName).bind("lastName");
        add(firstName, lastName);
    }

    public static class PersonBean {
        private String firstName;
        private String lastName;

        public String getFirstName() {
            return firstName;
        }

        public void setFirstName(String firstName) {
            this.firstName = firstName;
        }

        public String getLastName() {
            return lastName;
        }

        public void setLastName(String lastName) {
            this.lastName = lastName;
        }
    }

}