bug in project somewhere near NSJSONSerialization?

iOS newbie question here - I have been working through the blog reader app project and everything has been working great until I created a custom class (stage4) now every time I run my app it crashes in tableViewController.m at

 NSDictionary *dataDictionary = [NSJSONSerialization JSONObjectWithData:jsonData options:0 error: &error];

with the error "Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'data parameter is nil' "

I had a similar error earlier in the project when I made a typo in the URL but I have triple checked my syntax and haven't found any issues... To be sure I downloaded the project files for stage 5 (complete with exceptions for empty JSON data fields), ran them and it looks like the app is still crashing at exactly the same spot. This leads me to believe it is something different about xcode6 and JSON Serialization ? I've been reading through the apple documentation all morning and haven't found anything - although to be honest I am not entirely sure what I am looking for... Stumped, maybe I have missed something obvious but any pointers as to where/what to look for would be greatly appreciated!