I leave it to you to apply or not, but I think it makes things much clearer for new users. I think this patch is especially useful because it is no longer required to place #+LaTeX_Class: beamer at the top of the Org-mode file for beamer export. At least the "beamer" class and `org-latex-classes' should be mentioned in the beamer section of the manual. Additionally, I ran into another nil vs. empty string problem, which was fixed by the second patch attached.