Required field with no message shows empty tooltip

[aalmiray]

Setting a field with required(true) and no error message displays an empty tooltip when the field has no value. See attached screenshot

Here's the code that can reproduce the problem

import com.dlsc.formsfx.model.structure.Field;
import com.dlsc.formsfx.model.structure.Form;
import com.dlsc.formsfx.model.structure.Group;
import com.dlsc.formsfx.view.renderer.FormRenderer;
import javafx.application.Application;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;
import javafx.scene.Scene;
import javafx.stage.Stage;

public class Sample extends Application {
   @Override
   public void start(Stage stage) throws Exception {
      StringProperty p1 = new SimpleStringProperty("p1");
      StringProperty p2 = new SimpleStringProperty("p2");
      StringProperty p3 = new SimpleStringProperty("p3");
      StringProperty p4 = new SimpleStringProperty("p4");

      Form form = Form.of(
            Group.of(
                  Field.ofStringType(p1)
                        .label("P1")
                        .required(true),
                  Field.ofStringType(p2)
                        .label("P2")
                        .required(true),
                  Field.ofStringType(p3)
                        .label("P3")
                        .required(true),
                  Field.ofStringType(p4)
                        .label("P4")
                        .required(true)
            )
      );
      stage.setScene(new Scene(new FormRenderer(form)));
      stage.sizeToScene();
      stage.show();
   }
}