If it was me, I'd probably try to load the image, and handle the error that came back if it's missing with my fallback code. 

I always wind up going to google when I need an exception handler in Squeak. I don't need them often enough to remember the idiom, which is odd, coming from other languages. I think it falls out of the uniform object/message protocol, I suppose. If mostly the only error is "I didn't understand that message" and polymorphism is used pervasively, I guess exceptions only happen once in awhile. 

Is it weird that I'm surprised when exceptions only occur in exceptional circumstances? 

Anyway if you think an exception handler will give you what you want, I found an example for you here:

http://lists.squeakfoundation.org/pipermail/beginners/2008-September/005041.html

On Jan 22, 2011, at 10:53 AM, Mirko Kapps <mirkok.lists at googlemail.com> wrote:

> On 22.01.2011 19:30, Casey Ransberger wrote:
>> Cool:)
>> 
>> The reason I didn't put background on the default theme: I didn't know how big your display was. I think the default themes should supply a nice set of subtle gradients for the background, personally. This also keeps the image small.
>> 
>> That said, backgrounds add a lot of "friendly" and I could be completely wrong here; I'm grateful that Juan added background capabilities to the theme engine.
>> 
>> What do other people think?
> 
> Hi Casey.
> 
> Thanks for the theming. That's something that a newbie like me can easily start to play with! :-)
> 
> I too think that the default theme shouldn't have a background image (or at least a small seamless one that can be tilled). I just don't know yet how to do that or how to make a gradient (I currently learn about the Form class)
> 
> I'm also so brand new to Cuis that I don't know where to stop and not to exaggerate in adding feature (otherwise I had made #setbackground: to accept also an Array, so one can provide a Color or gradient as a fall-back in case the file is missing)
>