src/PubSub/Event.php
public function &offsetGet($key)
    {
        if ($this->hasValue($key)) {
            return $this->values[$key];
        }
        $null = null;
        return $null;
    }
public function &offsetGet($key)
    {
        if ($this->hasValue($key)) {
            return $this->values[$key];
        }
        $null = null;
        return $null;
    }
ArrayAccess getValue.

@param string $key Array key

@return mixed