lib/Yucca/Component/Selector/SelectorAbstract.php
public function currentShardingKey()
    {
        return isset($this->options[SelectorSourceInterface::SHARDING_KEY]) ? $this->options[SelectorSourceInterface::SHARDING_KEY] : null;
    }
public function currentShardingKey()
    {
        return isset($this->options[SelectorSourceInterface::SHARDING_KEY]) ? $this->options[SelectorSourceInterface::SHARDING_KEY] : null;
    }
Not applicable here, but for abstract purpose
@return null