public function setKey(?string $key)
    {
        $this->key = $key;
        $this->_key = null !== $key;

        return $this;
    }
public function setKey(?string $key)
    {
        $this->key = $key;
        $this->_key = null !== $key;

        return $this;
    }
Set key

@param string $key
@return object