Not true, it's dependant on the backlinks. If the domain has the backlinks to support the PR it will stay, if you get more backlinks it can rise and if you loose them it can drop.
Last update a few dozen PR domains i had most stayed, some went up (biggest was PR3-5) and others dropped a point or two.. None lost PR completely. What happens this update is anyones guess. Also i didn't read the Op's question correctly, he said it has no backlinks so SEO Ranter is right.. This particular domain is worthless and should lose it's PR.
I agree with the above, once i bought a PR 6 dropped domain and i optimize it on my own as well and it kept the PR value
Especially if they begin to start knocking off the paid link directories that a lot of people utilize to increase their PR. I imagine if a few of the big boys go down, it's going to cause an interesting domino effect within the industry.
I registered PR4 expired domain 3 monthe ago... and setup a blog... Since then I earned a lot from different ways (backlinks,paid reviews ,ads etc).. Still I'm earning because of Google PR updated delay..
Make sure it is a real PR domain and not a redirect or mirror site which has inherited pagerank from the real site. Sometimes its too good to be true to find a PR 5 and higher drop off domain.
If it is not showing any links then I believe that the PR will drop but I dont think it will be completely lost. Just dont pay tooo much of money for this.
However, google is not showing backlinks for a site but it has pr. If you check google webmaster tool then you can find backlinks of your site.