paperclip_assigning_empty_attachments.rb

# Setup
require 'active_record'
require 'paperclip'
require 'sqlite3'

ActiveRecord::Base.establish_connection(
    :adapter  => 'sqlite3',
    :database => ':memory:')

class AddTables < ActiveRecord::Migration
  include Paperclip::Schema
  def change
    create_table :things do |t|
      t.attachment :file
    end
  end
end

AddTables.migrate :up

class Thing < ActiveRecord::Base
  include Paperclip::Glue
  has_attached_file :file
end

# Test
original = Thing.create
copy = Thing.new
copy.file = original.file
copy.save

# Unexpectedly, the above results in a can't convert nil into String (TypeError) from paperclip