title: Carrierwave, MiniMagick - NoMethodError: undefined method `size' for nil:NilClass
body: <p>On staging, I'm facing the following error on uploading and resizing an image through carrierwave and minimagick. On local everything works fine.</p>
  
  <p>carrierwave (0.9.0)
  mini_magick (3.7.0)</p>
  
  <pre><code>irb(main):003:0&gt; PicturePost.create(remote_content_url: 'http://www.imagpress.com/img/slider/slider_1.jpg')
  NoMethodError: undefined method `size' for nil:NilClass
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/mini_magick-3.7.0/lib/mini_magick.rb:24:in `choose_processor'
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/mini_magick-3.7.0/lib/mini_magick.rb:64:in `mogrify?'
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/mini_magick-3.7.0/lib/mini_magick/image.rb:360:in `run_command'
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/mini_magick-3.7.0/lib/mini_magick/image.rb:171:in `valid?'
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/mini_magick-3.7.0/lib/mini_magick/image.rb:140:in `create'
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/mini_magick-3.7.0/lib/mini_magick/image.rb:48:in `read'
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/mini_magick-3.7.0/lib/mini_magick/image.rb:111:in `block in open'
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/mini_magick-3.7.0/lib/mini_magick/image.rb:110:in `open'
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/mini_magick-3.7.0/lib/mini_magick/image.rb:110:in `open'
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/carrierwave-0.9.0/lib/carrierwave/processing/mini_magick.rb:260:in `manipulate!'
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/carrierwave-0.9.0/lib/carrierwave/processing/mini_magick.rb:176:in `resize_to_fill'
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/carrierwave-0.9.0/lib/carrierwave/uploader/processing.rb:85:in `block in process!'
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/carrierwave-0.9.0/lib/carrierwave/uploader/processing.rb:81:in `each'
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/carrierwave-0.9.0/lib/carrierwave/uploader/processing.rb:81:in `process!'
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/carrierwave-0.9.0/lib/carrierwave/uploader/callbacks.rb:18:in `block in with_callbacks'
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/carrierwave-0.9.0/lib/carrierwave/uploader/callbacks.rb:18:in `each'
  9 levels...
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/carrierwave-0.9.0/lib/carrierwave/uploader/download.rb:65:in `download!'
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/carrierwave-0.9.0/lib/carrierwave/mount.rb:353:in `remote_url='
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/carrierwave-0.9.0/lib/carrierwave/mount.rb:203:in `remote_content_url='
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/carrierwave-0.9.0/lib/carrierwave/orm/activerecord.rb:44:in `remote_content_url='
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/activerecord-3.2.15/lib/active_record/attribute_assignment.rb:85:in `block in assign_attributes'
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/activerecord-3.2.15/lib/active_record/attribute_assignment.rb:78:in `each'
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/activerecord-3.2.15/lib/active_record/attribute_assignment.rb:78:in `assign_attributes'
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/activerecord-3.2.15/lib/active_record/base.rb:498:in `initialize'
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/activerecord-3.2.15/lib/active_record/persistence.rb:44:in `new'
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/activerecord-3.2.15/lib/active_record/persistence.rb:44:in `create'
  from (irb):3
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/railties-3.2.15/lib/rails/commands/console.rb:47:in `start'
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/railties-3.2.15/lib/rails/commands/console.rb:8:in `start'
  from /home/deploy/apps/staging/blog/shared/bundle/ruby/1.9.1/gems/railties-3.2.15/lib/rails/commands.rb:41:in `&lt;top (required)&gt;'
  from script/rails:6:in `require'
  </code></pre>
  
  <p>Can't figure out why this is happening.</p>