maint: Change the text of the NULLSTR() macro to "<null>"
maint: Change the text of the NULLSTR() macro to "<null>"

Eric Blake suggested to change this message to be different from the
glibc's NULL deref protection message in printf to be able to
differentiate errors.

eskultety/libvirt,andreabolognani/libvirt,taget/libvirt,elmarco/libvirt,taget/libvirt,eskultety/libvirt,rlaager/libvirt,agx/libvirt,rlaager/libvirt,datto/libvirt,rlaager/libvirt,shugaoye/libvirt,taget/libvirt,eskultety/libvirt,shugaoye/libvirt,taget/libvirt,fabianfreyer/libvirt,datto/libvirt,agx/libvirt,elmarco/libvirt,jardasgit/libvirt,agx/libvirt,VenkatDatta/libvirt,eskultety/libvirt,olafhering/libvirt,jardasgit/libvirt,zippy2/libvirt,jfehlig/libvirt,andreabolognani/libvirt,VenkatDatta/libvirt,libvirt/libvirt,zippy2/libvirt,olafhering/libvirt,nertpinx/libvirt,olafhering/libvirt,elmarco/libvirt,jardasgit/libvirt,crobinso/libvirt,crobinso/libvirt,rlaager/libvirt,crobinso/libvirt,jfehlig/libvirt,jfehlig/libvirt,libvirt/libvirt,VenkatDatta/libvirt,elmarco/libvirt,jardasgit/libvirt,zippy2/libvirt,shugaoye/libvirt,nertpinx/libvirt,VenkatDatta/libvirt,datto/libvirt,VenkatDatta/libvirt,andreabolognani/libvirt,shugaoye/libvirt,andreabolognani/libvirt,andreabolognani/libvirt,eskultety/libvirt,nertpinx/libvirt,libvirt/libvirt,nertpinx/libvirt,jardasgit/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,agx/libvirt,agx/libvirt,datto/libvirt,jfehlig/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,libvirt/libvirt,zippy2/libvirt,fabianfreyer/libvirt,olafhering/libvirt,rlaager/libvirt,datto/libvirt,taget/libvirt,crobinso/libvirt,shugaoye/libvirt,elmarco/libvirt