Hi,

while trying the new e-beamer I ran into a type-error which occurs when 
org-e-beamer-outline-frame-options is left at its default value `nil'.

The attached patch is a possible solution that works for me, though a 
more general check in org-e-beamer--normalize-arguments may be more 
appropriate (in case I'm not just missing to set a certain option 
right).

Regards,
Philipp