toJSON () {
        var obj = PropertyBase.toJSON(this);

        // remove value from file param if it's empty or non-string (can be non-serializable ReadStream)
        if (obj.type === 'file' && (typeof obj.value !== 'string' || !obj.value)) {
            _.unset(obj, 'value');
        }

        return obj;
    }
Convert the form-param to JSON compatible plain object.

@returns {Object}