Need to delete CarrierWave attachments with missing files - carrierwave

Question

We're working with an older Carrierwave installation and had an issue that caused many of our avatars to be deleted from the S3 bucket but they're still being referenced by Carrierwave. How can I safely clear out these broken instances without breaking our other user's avatars?
Version information:
Ruby 2.1.0
carrierwave-0.5.8
excon-0.32.0
fog-0.7.2
railties-3.2.18
I can't upgrade the gems any further at this point because there are other dependencies that will introduce breaking changes.
I've tried to instance.remove_avatar! functionality but that fails with the following error.
irb(main):041:0> t.remove_avatar!
Digest::Digest is deprecated; use Digest
[excon][WARNING] Invalid Excon request keys: :host
/app/vendor/bundle/ruby/2.1.0/gems/excon-0.32.0/lib/excon/connection.rb:389:in `validate_params'
/app/vendor/bundle/ruby/2.1.0/gems/excon-0.32.0/lib/excon/connection.rb:225:in `request'
/app/vendor/bundle/ruby/2.1.0/gems/fog-0.7.2/lib/fog/core/connection.rb:20:in `request'
/app/vendor/bundle/ruby/2.1.0/gems/fog-0.7.2/lib/fog/storage/aws.rb:323:in `request'
/app/vendor/bundle/ruby/2.1.0/gems/fog-0.7.2/lib/fog/storage/requests/aws/delete_object.rb:20:in `delete_object'
/app/vendor/bundle/ruby/2.1.0/gems/fog-0.7.2/lib/fog/storage/models/aws/file.rb:58:in `destroy'
/app/vendor/bundle/ruby/2.1.0/gems/carrierwave-0.5.8/lib/carrierwave/storage/fog.rb:178:in `delete'
/app/vendor/bundle/ruby/2.1.0/gems/carrierwave-0.5.8/lib/carrierwave/uploader/remove.rb:15:in `block in remove!'
/app/vendor/bundle/ruby/2.1.0/gems/carrierwave-0.5.8/lib/carrierwave/uploader/callbacks.rb:17:in `with_callbacks'
/app/vendor/bundle/ruby/2.1.0/gems/carrierwave-0.5.8/lib/carrierwave/uploader/remove.rb:14:in `remove!'
/app/vendor/bundle/ruby/2.1.0/gems/carrierwave-0.5.8/lib/carrierwave/mount.rb:365:in `remove!'
/app/vendor/bundle/ruby/2.1.0/gems/carrierwave-0.5.8/lib/carrierwave/mount.rb:205:in `remove_avatar!'
(irb):41:in `irb_binding'
/app/vendor/ruby-2.1.0/lib/ruby/2.1.0/irb/workspace.rb:86:in `eval'
/app/vendor/ruby-2.1.0/lib/ruby/2.1.0/irb/workspace.rb:86:in `evaluate'
/app/vendor/ruby-2.1.0/lib/ruby/2.1.0/irb/context.rb:380:in `evaluate'
/app/vendor/ruby-2.1.0/lib/ruby/2.1.0/irb.rb:492:in `block (2 levels) in eval_input'
/app/vendor/ruby-2.1.0/lib/ruby/2.1.0/irb.rb:624:in `signal_status'
/app/vendor/ruby-2.1.0/lib/ruby/2.1.0/irb.rb:489:in `block in eval_input'
/app/vendor/ruby-2.1.0/lib/ruby/2.1.0/irb/ruby-lex.rb:247:in `block (2 levels) in each_top_level_statement'
/app/vendor/ruby-2.1.0/lib/ruby/2.1.0/irb/ruby-lex.rb:233:in `loop'
/app/vendor/ruby-2.1.0/lib/ruby/2.1.0/irb/ruby-lex.rb:233:in `block in each_top_level_statement'
/app/vendor/ruby-2.1.0/lib/ruby/2.1.0/irb/ruby-lex.rb:232:in `catch'
/app/vendor/ruby-2.1.0/lib/ruby/2.1.0/irb/ruby-lex.rb:232:in `each_top_level_statement'
/app/vendor/ruby-2.1.0/lib/ruby/2.1.0/irb.rb:488:in `eval_input'
/app/vendor/ruby-2.1.0/lib/ruby/2.1.0/irb.rb:397:in `block in start'
/app/vendor/ruby-2.1.0/lib/ruby/2.1.0/irb.rb:396:in `catch'
/app/vendor/ruby-2.1.0/lib/ruby/2.1.0/irb.rb:396:in `start'
/app/vendor/bundle/ruby/2.1.0/gems/railties-3.2.18/lib/rails/commands/console.rb:47:in `start'
/app/vendor/bundle/ruby/2.1.0/gems/railties-3.2.18/lib/rails/commands/console.rb:8:in `start'
/app/vendor/bundle/ruby/2.1.0/gems/railties-3.2.18/lib/rails/commands.rb:41:in `<top (required)>'
script/rails:6:in `require'
script/rails:6:in `<main>'
=> [:remove_versions!]
I've opened up an issue on Carrierwave's Github tracker as well.

Answer 1

I'm going to close the issue as we were able to work around.
I'd forgotten to mentioned that we are also using the carrierwave-mongoid. Which I think saved our butt.
By setting the instance avatar manually then resaving the model and ignoring the Excon error we forced the models to use their default image.
So in this case, given we have an instance of a model named t.
> t[:avatar] = nil
> t.save rescue nil
This changed the avatar.url to resolve as the default image.