Unable to connect to friend's game on the dev server

I'm trying to connect to my friend's game on the dev server but when I try to connect I'm getting the error "NoMethodError: undefined method `[]' for nil:NilClass". The bookmark I use takes me to the campaign details page and normally it has worked just fine. Any idea what I need to do to fix this?

Ok, so you have joined the game before? 

Please send me the join link. 

- Gauss

Thanks for the reply Gauss but it looks like the GM has fixed it.