Newbie saying hello.

Hi all, just wanted to introduce myself to the list. 
I'm a recent graduate who's teaching myself a bit of C (they taught us
java - bah!) and working on a project involving libdvdread. 

First up, thanks! The project I have to do is very DVD based and the
library is going to save me massive amounts of effort.

Now, I'm a bit of a C newbie, so please be gentle if this is a stoopid
question but I've just spent ages trapping a bug in one of my test
programs. Problem was I was accidentally passing a null pointer as the
data argument to DVDReadBlocks() (I said I was a newbie!). My question
then is would it incur an excessive performance hit for playback
purposes to do a not null check on the data argument to the
DVDReadXXXX() functions?

If not, this is something I'd be happy to implement, it being something
I could probably just about cope with ;) and a way of contributing
something to a really great project.

Cheers for listening

Bryn