Yeah, figured it may cause some problems, but would get you over any Fatal Error blues in the short term. Didn't have the code directly in front of me at the time. If it's a PHP warning about something not being an array, you can try updating "null" to "array();":
Looking at it, I think that's the better way to do it. However, if you're seeing something else, let us know... we hate warnings and anything else PHP can spit out, so we'll help you fix it.. and it will help us get it ready to have in the next release anyways.
We'll investigate this in the next day or so to see if we can figure out the best way to support JomSocial 1.8 and below, and let you know what we find.. but if you run into other problems related to this, or anything else, in the meantime, just let us know.
Alex