Question

I’m getting this error with the Paperclip gem.

NoMethodError (You have a nil object when you didn't expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.size):
  paperclip (2.3.8) lib/paperclip/attachment.rb:104:in `assign'

How can I debug this, seeing as though it’s in a gem? If this was my code I would place a few puts to see what’s going on, but I can’t do that here. I’m using Rails 3.0.1

Answer 1

here’s my best shot.

• Open one of your controllers and add a debugger line to it. We need the debugger to kick in to set the breakpoint
• Next run rails --debug
• navigate to the page / controller with the breakpoint
• the debugger console will appear.
• run Gem.find_files("attachment.rb") <- I’ll call $GEM_ROOT to the path that this returns
• run list $GEM_ROOT/lib/paperclip/attachment.rb:104 – this will show the code around the area where the error occurred.
• run b $GEM_ROOT/lib/paperclip/attachment.rb:$LINE – replace $LINE for a good candidate for the breakpoint.
• run cont
• hit the page / action that causes the error, and the debug console should open at the break point.

I think there must be a way to get the path to the gem file programmatically, but I have no idea how to do it 🙁