framework/behaviors/BlameableBehavior.php
protected function getDefaultValue($event)
    {
        if ($this->defaultValue instanceof \Closure || (is_array($this->defaultValue) && is_callable($this->defaultValue))) {
            return call_user_func($this->defaultValue, $event);
        }

        return $this->defaultValue;
    }
protected function getDefaultValue($event)
    {
        if ($this->defaultValue instanceof \Closure || (is_array($this->defaultValue) && is_callable($this->defaultValue))) {
            return call_user_func($this->defaultValue, $event);
        }

        return $this->defaultValue;
    }
Get default value
@param \yii\base\Event $event
@return array|mixed
@since 2.0.14