As I told about, during upgrading from 4.2 (I am testing from 4.3) many errors occurs. This threated in a global way in id4377.
Here the problem comes from tra.php this generates a fatal ERROR
Reason during first tiki-setup tra.php can be called when $tikilib is not yet set then the function tra_impl crashes.
It seems that at this stage of installation (managing session prefs) is it, as if getone() should answer false, nothing particular to do :
I have justed added a first level isset on $tikilib
See the joined patched source with comments.