[FLOW3-general] Image resource

[Georg Ortner]

I've a question regarding to the Image resource in the getting started 
tutorial:

If I don't pick a Image in the form to create a new Blog I'm getting 
this exception:

#1259748358: A valid sha1 hash must be passed to this constructor.

Of course there is no valid sha1 hash of an image because there is no 
image! Is this how it's supposed to be? How can I create a form for a 
model which can have an image which isn't mandatory?

thanks