Grails - Calling built in constraint from custom validator closure

I'd like to be able to have a constraint implemented as optional based on another field of the domain class.

Such that, if importModeis true, the company field is no longer required, but if import mode is false the default functionality provided by company (blank:false) is invoked.

class MyClass {
    boolean importMode
    String company

    static constraints = {
        company(validator: { val, obj ->
            if(obj.importMode) {
                // return default blank:false functionality
            }
            return true // else pass
        }
    }
}

Is it possible in Grails to call the built in constraints from a custom constraint closure like this?

You have to define a custom constraint, not use the default nullable or blank constraint

class MyClass {
    boolean importMode
    String company

    static constraints = {
        company(validator: { val, obj ->
            if(!obj.importMode && !val) {
              return['myClass.company.required']
            }
        })
    }
}