User Error

This code goes in {ModelName}::beforeSave:

foreach ($this->data[$this->name] as $key => $value) {
    if (!set::classicExtract($this->data,$this->name . '.' . $key)) {
        $this->data = set::remove($this->data,$this->name . '.' . $key);
    }
}

I use it where the DB may be expecting values for certain fields that are optional in the UI, and therefore may be returned empty by the controller.