PackageManager::createPackage is incompatible to PackageManagerInterface
The last parameter must be of type NULL, but is of type string. Either change the interface or set the default value inside the method instead of inside the signature.
As the parameter is supposed to be of type string, I suggest to just change the interface signature to an empty string instead of NULL - at least this is what is to be expected from the phpdoc comment.
Please note that this also fatals in PHP 5.5.7 (Fedora 19) for the CMS Core unit tests which also use this implementation.
#hhvm also chokes about this