class Photo < ActiveRecord::Base
  has_dynamic_attached_file :image, styles: { thumb: '100x100#' }
end

class Photo < ActiveRecord::Base
  has_dynamic_attached_file :image, styles: { thumb: '100x100#' }
  do_not_validate_attachment_file_type :image
end

Add do_not_validate_attachment_file_type to dummy Photo model to keep newer Paperclip from raising errors since we don't validate the attachment
Add do_not_validate_attachment_file_type to dummy Photo model to keep newer Paperclip from raising errors since we don't validate the attachment
