@NotNull not validated with Vaadin 8

Hi, I noticed that the annotation @NotNull does not cause a validation error on its field when there is no value.
The required indicator is shown but if I enter text and immediately erase it, the field validation is not fired (field is not red with exclamation point). Doing the same with @Size works thought…

Enabling a Save button with the validation result will do the same. The button will be enabled even if the field value is empty.

I use BeanValidationBinder on Vaadin 8. Here is an example of bean field.

@NotNull         //not triggered but required indicator shown
@Size(max = 5)   //triggered
private String name;