The \Magento\Framework\App\Config\ScopePool::_getScopeCode() method has a wrong PHPDoc type for the $scopeCode parameter

https://github.com/magento/magento2/blob/2.0.0/lib/internal/Magento/Framework/App/Config/ScopePool.php#L107-L127

Should be:

@param null|string|int|\Magento\Framework\App\ScopeInterface $scopeCode [optional]

Also please note that \Magento\Framework\DataObject part in the type is wrong because in this case the result of the method will be equal to $scopeCode, but the method should return a string, not \Magento\Framework\DataObject.

https://github.com/magento/magento2/issues/2857

See also: