BindingBuilder.asRequired() returns true for nulls

[mvysny]

Vaadin 8.6.3. I have the following binder setup:

        final Binder<Person> binder = new Binder<>(Person.class);
        final TextField name = new TextField();
        name.setCaption("Type your name here:");
        binder.forField(name).withNullRepresentation("").asRequired().bind("name");

The problem is that with this setup, an empty TextField passes the asRequired() validation and null is passed into Person.setName() with the following code:

if (binder.isValid() && binder.writeBeanIfValid(p)) { 
  // all ok
}

[mvysny]

vaadin-app.zip
Attaching a project reproducing the issue.

[TatuLund]

Default implementation of asRequired() is a short hand for the following

See: https://github.com/vaadin/framework/blob/master/server/src/main/java/com/vaadin/data/Binder.java#L912

asRequired(Validator.from(value -> !Objects.equals(value, field.getEmptyValue())

The method with custom asRequired validator is also public, see

https://vaadin.com/api/framework/8.6.3/com/vaadin/data/Binder.BindingBuilder.html#asRequired-com.vaadin.data.Validator-

Which gives a workaround

asRequired(Validator.from(value -> (value != null && !Objects.equals(value, field.getEmptyValue()))

[mvysny]

Thank you for posting the workaround. Yet I believe that nulls effectively mean "no value" and thus the standard asRequired() method should catch them in addition with the empty value, exactly as your workaround suggests.

[stale]

Hello there!

We are sorry that this issue hasn't progressed lately. We are prioritizing issues by severity and the number of customers we expect are experiencing this and haven't gotten around to fix this issue yet.

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[Legioth]

I think there's an even easier workaround, but I'm too lazy to test it in practice. The null representation converter and the required validator are forming a processing chain where order matters. If you change the order between validator and the converter, then the validator will see the original value from the field (i.e. "") rather than null and thus fail validation.

binder.forField(name).asRequired().withNullRepresentation("").bind("name");

[NetRob]

I think there's an even easier workaround, but I'm too lazy to test it in practice. The null representation converter and the required validator are forming a processing chain where order matters. If you change the order between validator and the converter, then the validator will see the original value from the field (i.e. "") rather than null and thus fail validation.

binder.forField(name).asRequired().withNullRepresentation("").bind("name");

setting asRequired before withNullRepresentation actually solves it for me 👍
(tested in Vaadin 14 with an required Long value)