kartik\builder\FormTrait::checkFormConfig PHP Method

    protected function checkFormConfig()
    {
        if (!$this->hasModel() && empty($this->formName)) {
            throw new InvalidConfigException("Either the 'formName' has to be set or a valid 'model' property must be set extending from '\\yii\\base\\Model'.");
        }
        if (empty($this->formName) && (empty($this->form) || !$this->form instanceof ActiveForm)) {
            throw new InvalidConfigException("The 'form' property must be set and must be an instance of '\\kartik\\form\\ActiveForm'.");
        }
    }