delayed_job: undefined method `name' for nil:NilClass - ruby-on-rails-3

Question

I just installed delayed job on my little Rails 3.2 app. Here is the controller where I use it:
require 'waveform'
class MixesController < ApplicationController
def index
end
def new
#mix = Mix.new
end
def create
#mix = Mix.new(params[:mix])
if #mix.save
options = {
method: :rms,
width: 1800,
height: 280,
background_color: "#ffffff",
color: "#3333ff",
force: true,
quiet: true
}
waveform = "./public/waveforms/#{File.basename(#mix.sound_file.to_s, File.extname(#mix.sound_file.to_s))}.png"
::Waveform.new("./public" + #mix.sound_file.to_s, nil).delay.generate(waveform, options)
flash[:success] = "Mix successfully uploaded"
redirect_to mix_url(#mix)
else
render :new
end
end
def show
#mix = Mix.find(params[:id])
end
end
I get an error saying: undefined methodname' for nil:NilClass`, here is the full stack trace:
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:25:in `block in initialize'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:27:in `yield'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:27:in `default'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:27:in `block in initialize'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:27:in `yield'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:27:in `default'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:27:in `block in initialize'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:27:in `yield'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:27:in `default'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:27:in `block in initialize'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:27:in `yield'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:27:in `default'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:27:in `block in initialize'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:102:in `yield'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:102:in `default'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:102:in `accept'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:447:in `block in dump_ivars'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:445:in `each'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:445:in `dump_ivars'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:124:in `visit_Object'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:102:in `accept'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:434:in `block in emit_coder'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:432:in `each'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:432:in `emit_coder'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:417:in `dump_coder'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:100:in `accept'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/visitors/yaml_tree.rb:66:in `push'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych.rb:242:in `dump'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/psych/core_ext.rb:14:in `psych_to_yaml'
delayed_job (3.0.3) lib/delayed/backend/base.rb:80:in `payload_object='
activerecord (3.2.3) lib/active_record/attribute_assignment.rb:85:in `block in assign_attributes'
activerecord (3.2.3) lib/active_record/attribute_assignment.rb:78:in `each'
activerecord (3.2.3) lib/active_record/attribute_assignment.rb:78:in `assign_attributes'
activerecord (3.2.3) lib/active_record/base.rb:498:in `initialize'
delayed_job (3.0.3) lib/delayed/backend/base.rb:28:in `new'
delayed_job (3.0.3) lib/delayed/backend/base.rb:28:in `enqueue'
delayed_job (3.0.3) lib/delayed/message_sending.rb:13:in `method_missing'
app/controllers/mixes_controller.rb:25:in `create'
actionpack (3.2.3) lib/action_controller/metal/implicit_render.rb:4:in `send_action'
actionpack (3.2.3) lib/abstract_controller/base.rb:167:in `process_action'
actionpack (3.2.3) lib/action_controller/metal/rendering.rb:10:in `process_action'
actionpack (3.2.3) lib/abstract_controller/callbacks.rb:18:in `block in process_action'
activesupport (3.2.3) lib/active_support/callbacks.rb:414:in `_run__842168672059661955__process_action__4066633601342968686__callbacks'
activesupport (3.2.3) lib/active_support/callbacks.rb:405:in `__run_callback'
activesupport (3.2.3) lib/active_support/callbacks.rb:385:in `_run_process_action_callbacks'
activesupport (3.2.3) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (3.2.3) lib/abstract_controller/callbacks.rb:17:in `process_action'
actionpack (3.2.3) lib/action_controller/metal/rescue.rb:29:in `process_action'
actionpack (3.2.3) lib/action_controller/metal/instrumentation.rb:30:in `block in process_action'
activesupport (3.2.3) lib/active_support/notifications.rb:123:in `block in instrument'
activesupport (3.2.3) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (3.2.3) lib/active_support/notifications.rb:123:in `instrument'
actionpack (3.2.3) lib/action_controller/metal/instrumentation.rb:29:in `process_action'
actionpack (3.2.3) lib/action_controller/metal/params_wrapper.rb:205:in `process_action'
activerecord (3.2.3) lib/active_record/railties/controller_runtime.rb:18:in `process_action'
actionpack (3.2.3) lib/abstract_controller/base.rb:121:in `process'
actionpack (3.2.3) lib/abstract_controller/rendering.rb:45:in `process'
actionpack (3.2.3) lib/action_controller/metal.rb:203:in `dispatch'
actionpack (3.2.3) lib/action_controller/metal/rack_delegation.rb:14:in `dispatch'
actionpack (3.2.3) lib/action_controller/metal.rb:246:in `block in action'
actionpack (3.2.3) lib/action_dispatch/routing/route_set.rb:73:in `call'
actionpack (3.2.3) lib/action_dispatch/routing/route_set.rb:73:in `dispatch'
actionpack (3.2.3) lib/action_dispatch/routing/route_set.rb:36:in `call'
journey (1.0.3) lib/journey/router.rb:68:in `block in call'
journey (1.0.3) lib/journey/router.rb:56:in `each'
journey (1.0.3) lib/journey/router.rb:56:in `call'
actionpack (3.2.3) lib/action_dispatch/routing/route_set.rb:600:in `call'
actionpack (3.2.3) lib/action_dispatch/middleware/best_standards_support.rb:17:in `call'
rack (1.4.1) lib/rack/etag.rb:23:in `call'
rack (1.4.1) lib/rack/conditionalget.rb:35:in `call'
actionpack (3.2.3) lib/action_dispatch/middleware/head.rb:14:in `call'
actionpack (3.2.3) lib/action_dispatch/middleware/params_parser.rb:21:in `call'
actionpack (3.2.3) lib/action_dispatch/middleware/flash.rb:242:in `call'
rack (1.4.1) lib/rack/session/abstract/id.rb:205:in `context'
rack (1.4.1) lib/rack/session/abstract/id.rb:200:in `call'
actionpack (3.2.3) lib/action_dispatch/middleware/cookies.rb:338:in `call'
activerecord (3.2.3) lib/active_record/query_cache.rb:64:in `call'
activerecord (3.2.3) lib/active_record/connection_adapters/abstract/connection_pool.rb:467:in `call'
actionpack (3.2.3) lib/action_dispatch/middleware/callbacks.rb:28:in `block in call'
activesupport (3.2.3) lib/active_support/callbacks.rb:405:in `_run__647780415925652457__call__1911592835196459847__callbacks'
activesupport (3.2.3) lib/active_support/callbacks.rb:405:in `__run_callback'
activesupport (3.2.3) lib/active_support/callbacks.rb:385:in `_run_call_callbacks'
activesupport (3.2.3) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (3.2.3) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
actionpack (3.2.3) lib/action_dispatch/middleware/reloader.rb:65:in `call'
actionpack (3.2.3) lib/action_dispatch/middleware/remote_ip.rb:31:in `call'
actionpack (3.2.3) lib/action_dispatch/middleware/debug_exceptions.rb:16:in `call'
actionpack (3.2.3) lib/action_dispatch/middleware/show_exceptions.rb:56:in `call'
railties (3.2.3) lib/rails/rack/logger.rb:26:in `call_app'
railties (3.2.3) lib/rails/rack/logger.rb:16:in `call'
actionpack (3.2.3) lib/action_dispatch/middleware/request_id.rb:22:in `call'
rack (1.4.1) lib/rack/methodoverride.rb:21:in `call'
rack (1.4.1) lib/rack/runtime.rb:17:in `call'
activesupport (3.2.3) lib/active_support/cache/strategy/local_cache.rb:72:in `call'
rack (1.4.1) lib/rack/lock.rb:15:in `call'
actionpack (3.2.3) lib/action_dispatch/middleware/static.rb:62:in `call'
railties (3.2.3) lib/rails/engine.rb:479:in `call'
railties (3.2.3) lib/rails/application.rb:220:in `call'
rack (1.4.1) lib/rack/content_length.rb:14:in `call'
railties (3.2.3) lib/rails/rack/log_tailer.rb:14:in `call'
rack (1.4.1) lib/rack/handler/webrick.rb:59:in `service'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/httpserver.rb:138:in `service'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/httpserver.rb:94:in `run'
/Users/aziz/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/server.rb:191:in `block in start_thread'
Does anyone know why I am getting this error please?

Answer 1

This is happening because the system is trying to turn nil into a value that can be stored in YAML and is failing.
Looking at your code, I expect that is because you are passing a nil object into the variables passed to Waveform.new (the method whose operation is being delayed). The variables passed to new will need to be stored until delayed job is ready to run the process, and I expect they are stored as YAML.
Can you refactor Waveform to either make the second attribute optional (so its value doesn't have to be preserved)
::Waveform.new("./public" + #mix.sound_file.to_s).delay.generate(waveform, options)
or use something else to have the same meaning as nil. For example, pass in the symbol :none. Then the line becomes:
::Waveform.new("./public" + #mix.sound_file.to_s, :none).delay.generate(waveform, options)