Validator configuration is not working when using validators in Blossom dialogs

If a validator is configured for a field inside a Blossom dialog, a template error occurs when the dialog gets loaded for editing. The dialog cannot be opened.

The cause for this error is the getValidatorName() method in the class

info.magnolia.ui.form.validator.definition.FieldValidatorDefinitionKeyGenerator

In line 45 the getName() method of the ConfiguredFieldValidatorDefinition instance is called. This returns null for a validator configured with Blossom. When null is passed to the of method of Optional, a NullPointerException is thrown:

return definition instanceof ConfiguredFieldValidatorDefinition?
Optional.of(((ConfiguredFieldValidatorDefinition)definition).getName()):Optional.empty();

Example code:

@TabFactory("Content")
public void contentTab(UiConfig cfg, TabBuilder tab, DialogCreationContext context) throws InvalidPathException {

tab.fields(
    cfg.fields.text("items").label("Number of items").defaultValue("10").validator(cfg.validators.digitsOnly()));

}

This bug is related to an already existing open issue in #BLOSSOM-245