If the user tries to read a pathstring pointing to node1, since that node is system reserved and should be acessible, eZP should return an exception like:

throw new Exception( "Invalid node id. The node 1 is system reserved and can`t be loaded." )

Steps to reproduce

Try execute the code below in a situation where the pathstring is /1/:

return new Subtree($this->locationService->loadLocation($locationId)->pathString);

^{Please notice that there's a related documentation issue: EZP-26912}