title: carrierwave upload Encoding::UndefinedConversionError: "\xFF" from ASCII-8BIT to UTF-8
body: <p>Got this error on production but can't figure out where the problem is. Same request works fine on local development. But fail on production. I'm building API for mobile client use</p>
  
  <h3>Error trace</h3>
  
  <p>```</p>
  
  <pre><code>Encoding::UndefinedConversionError: "\xFF" from ASCII-8BIT to UTF-8
  ... 39 non-project frames
  File"/home/deploy/.bundler/example/ruby/2.0.0/gems/activesupport4.1.0/lib/active_support/core_ext/object/json.rb" line 34 in encode
  File"/home/deploy/.bundler/example/ruby/2.0.0/gems/activesupport4.1.0/lib/active_support/core_ext/object/json.rb" line 34 in to_json
  File"/home/deploy/.bundler/example/ruby/2.0.0/gems/activesupport4.1.0/lib/active_support/core_ext/object/json.rb" line 34 in to_json_with_active_support_encoder
  File"/home/deploy/.bundler/example/ruby/2.0.0/gems/activesupport4.1.0/lib/active_support/json/encoding.rb" line 56 in to_json
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/json-1.8.1/lib/json/common.rb" line 223 in generate
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/json-1.8.1/lib/json/common.rb" line 223 in generate
  File"/home/deploy/.bundler/example/ruby/2.0.0/gems/activesupport4.1.0/lib/active_support/json/encoding.rb" line 96 in stringify
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/activesupport4.1.0/lib/active_support/json/encoding.rb" line 34 in encode
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/activesupport-4.1.0/lib/active_support/json/encoding.rb" line 21 in encode
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/activesupport-4.1.0/lib/active_support/core_ext/object/json.rb" line 37 in to_json_with_active_support_encoder
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/multi_json-1.10.1/lib/multi_json/adapters/json_common.rb" line 21 in dump
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/multi_json-1.10.1/lib/multi_json/adapter.rb" line 24 in dump
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/multi_json-1.10.1/lib/multi_json.rb" line 136 in dump
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/rollbar-0.12.20/lib/rollbar.rb" line 437 in build_payload
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/rollbar-0.12.20/lib/rollbar.rb" line 95 in report_exception
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/rollbar-0.12.20/lib/rollbar/exception_reporter.rb" line 9 in report_exception_to_rollbar
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/rollbar-0.12.20/lib/rollbar/middleware/rails/show_exceptions.rb" line 22 in rescue in call_with_rollbar
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/rollbar-0.12.20/lib/rollbar/middleware/rails/show_exceptions.rb" line 19 in call_with_rollbar
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/actionpack-4.1.0/lib/action_dispatch/middleware/show_exceptions.rb" line 30 in call
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/railties-4.1.0/lib/rails/rack/logger.rb" line 38 in call_app
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/railties-4.1.0/lib/rails/rack/logger.rb" line 20 in block in call
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/activesupport-4.1.0/lib/active_support/tagged_logging.rb" line 68 in block in tagged
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/activesupport-4.1.0/lib/active_support/tagged_logging.rb" line 26 in tagged
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/activesupport-4.1.0/lib/active_support/tagged_logging.rb" line 68 in tagged
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/railties-4.1.0/lib/rails/rack/logger.rb" line 20 in call
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/actionpack-4.1.0/lib/action_dispatch/middleware/request_id.rb" line 21 in call
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/rack-1.5.2/lib/rack/methodoverride.rb" line 21 in call
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/rack-1.5.2/lib/rack/runtime.rb" line 17 in call
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/activesupport-4.1.0/lib/active_support/cache/strategy/local_cache_middleware.rb" line 26 in call
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/rack-1.5.2/lib/rack/sendfile.rb" line 112 in call
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/railties-4.1.0/lib/rails/engine.rb" line 514 in call
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/railties-4.1.0/lib/rails/application.rb" line 144 in call
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/unicorn-4.8.2/lib/unicorn/http_server.rb" line 572 in process_client
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/unicorn-4.8.2/lib/unicorn/http_server.rb" line 666 in worker_loop
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/unicorn-4.8.2/lib/unicorn/http_server.rb" line 521 in spawn_missing_workers
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/unicorn-4.8.2/lib/unicorn/http_server.rb" line 140 in start
  File "/home/deploy/.bundler/example/ruby/2.0.0/gems/unicorn-4.8.2/bin/unicorn_rails" line 209 in &lt;top (required)&gt;
  File "/home/deploy/.bundler/example/ruby/2.0.0/bin/unicorn_rails" line 23 in load
  File "/home/deploy/.bundler/example/ruby/2.0.0/bin/unicorn_rails" line 23 in &lt;main&gt;
  </code></pre>
  
  <p>```</p>
  
  <h1>controller is pretty simple</h1>
  
  <p>```</p>
  
  <pre><code>  def create
      @work = current_user.works.build(permitted_params.work)
      if @work.save
        render json: @work, status: :created
      else
        render json: { status: 'error', message: @work.errors.full_messages }, status: :bad_request
      end
    end
  </code></pre>
  
  <p>```</p>
  
  <h1>raw request body</h1>
  
  <p>```</p>
  
  <pre><code>POST /api/my/works HTTP/1.1
  Host: example.com
  Cache-Control: no-cache
  Postman-Token: 98f4ce29-a72e-53e9-98e6-d08bbc4ca6f1
  Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryp7MA4YWxkTrZu0gW
  
  ----WebKitFormBoundaryE19zNvXGzXaLvS5C
  Content-Disposition: form-data; name="auth_token"
  
  0e008b699c8904c26cba54ac54a5bb49
  ----WebKitFormBoundaryE19zNvXGzXaLvS5C
  Content-Disposition: form-data; name="name"
  
  blah
  ----WebKitFormBoundaryE19zNvXGzXaLvS5C
  Content-Disposition: form-data; name="cover_image"; filename="IMG_1755.JPG"
  Content-Type: image/jpeg
  
  
  ----WebKitFormBoundaryE19zNvXGzXaLvS5C
  Content-Disposition: form-data; name="model"
  
  iPad Air
  ----WebKitFormBoundaryE19zNvXGzXaLvS5C
  Content-Disposition: form-data; name="work_type"
  
  is_public
  ----WebKitFormBoundaryE19zNvXGzXaLvS5C
  </code></pre>
  
  <p>```</p>
  
  <h1>enviroments</h1>
  
  <p>Rails 4.1.1
  Ruby 2.0</p>