How to update "has-value" attribute in the custom field.

BinderDemoView.java

package org.tatu.vaadin20.views;

import com.vaadin.flow.component.button.Button;
import com.vaadin.flow.component.customfield.CustomField;
import com.vaadin.flow.component.html.Span;
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;

@Route(value = "binder")
public class BinderDemoView extends VerticalLayout {
    private Binder<Pojo> binder = new Binder<>();
    private Pojo pojo;

    public BinderDemoView() {
        pojo = new Pojo("Pojo example", "value1", "value2");
        buildUI();
    }

    private void buildUI() {
        add(new Span("Binder demo"));

        CustomTextField name = new CustomTextField();
        name.setLabel("Name");
        CustomTextField field1 = new CustomTextField();
        field1.setLabel("Field 1");
        TextField field2 = new TextField();
        field2.setLabel("Field 2");

        add(name, field1, field2);

        binder.forField(name).bind(Pojo::getName, Pojo::setName);
        binder.forField(field1).asRequired("is Required").bind(Pojo::getField1,
                Pojo::setField1);
        binder.forField(field2).asRequired("is Required").bind(Pojo::getField2,
                Pojo::setField2);

        Button setBean = new Button("Set Bean", event -> {
            setBean();
        });

        add(setBean);
    }

    public void setBean() {
        binder.setBean(pojo);
    }

    public static class CustomTextField extends CustomField<String> {
        private TextField mainComponent = new TextField();

        public CustomTextField() {
            add(mainComponent);
            // Workaround
            this.addValueChangeListener(event -> {
                if (event.getValue() != null) {
                    getElement().setAttribute("has-value", true);
                } else {
                    getElement().removeAttribute("has-value");
                }
            });
        }

        @Override
        public void setInvalid(boolean invalid) {
            super.setInvalid(invalid);
            mainComponent.setInvalid(invalid);
        }

        @Override
        protected String generateModelValue() {
            if (mainComponent.getValue().isEmpty()) {
                return null;
            }
            return mainComponent.getValue();
        }

        @Override
        protected void setPresentationValue(String newPresentationValue) {
            if (newPresentationValue == null) {
                newPresentationValue = "";
            }
            mainComponent.setValue(newPresentationValue);
        }
    }

    public static class Pojo {
        private String Name;
        private String field1;
        private String field2;

        public Pojo(String name, String field1, String field2) {
            Name = name;
            this.field1 = field1;
            this.field2 = field2;
        }

        public String getName() {
            return Name;
        }

        public void setName(String name) {
            Name = name;
        }

        public String getField1() {
            return field1;
        }

        public void setField1(String field1) {
            this.field1 = field1;
        }

        public String getField2() {
            return field2;
        }

        public void setField2(String field2) {
            this.field2 = field2;
        }
    }
}