Adding a rule to a custom rule in Eureka

So I've created a custom row which is just a row with a simply UITextView now I want to create a rule such that if the UITextView has under 100 characters the variable row.isValid will evaluate to false.

<<< TextViewRow("About Me") {
    let cell = $0.baseCell as! TextViewCell
    cell.textView.text = currentUser.aboutMe
    $0.disabled = Condition.function([]) {
        form in
        print("in disabled")
        let section = form.sectionBy(tag: "About Me")
        let view = section!.header?.viewForSection(section!, type: .header) as! TitleHeaderView
        if view.isLocked {
            return true
        } else {
            return false
        }
    }
    $0.cellUpdate({ (cell, row) in
        if row.isDisabled {
            cell.textView.isUserInteractionEnabled = false
            cell.textView.textColor = UIColor.gray
        } else {
            cell.textView.isUserInteractionEnabled = true
            cell.textView.textColor = UIColor.black
        }
    })
    let ruleRequiredViaClosure = RuleClosure<String> { rowValue in
        guard let rowValue = rowValue else {
            return(ValidationError(msg : "Please write more!"))
        }
        let numberOfCharacters = rowValue.characters.count
        return (numberOfCharacters < 250 ? ValidationError(msg: "Please write more!") : nil)
    }
    $0.add(rule: ruleRequiredViaClosure)
    $0.validationOptions = .validatesOnDemand
}

With a normal TextRow this would compile and XCode won't throw any error, although since TextViewRow is a custom row I believe this is why it is throwing an error.

The error it gives me is that I need to use:

$0.add(ruleSet: ...)

but I can't find any documentation on it.

Also I'm not sure whether I am able to define my rule as I have since the rowValue in the closure probably isn't referencing anything. How would I fix this problem?