fix consistent configuration bug: falsy value (0, false) cannot be identified

When using placeholder in consistent configuration, falsy value cannot be replaced. For example:
in js file, you declare a car bean:
var Car = function() {
    this.isBroken = null;
}
module.exports = {
    id : 'car',
    func : Car,
    props : [{
        name : 'isBroken',
        value : '${car.broken}‘
    }]
}

When you put car.broken into false, your isBroken will be ${car.broken}.