title: rake aborted! undefined method `[]' for nil:NilClass
body: <p>I get this error when I try to precompile assets. I'm fairly new to Rails and dealing with the asset pipeline makes me want to pull my hair out, lol. I get this same error trying it with ruby 1.9.2-p320, or ruby 1.9.3-p448. Using Rails 3.2.13. The hard part for me is looking at the error output and understanding where to look for the error. I don't see a lot of explanations on how to do that. Am I correct that the error is in a rails helper file? If so, where is that?</p>
  
  <pre><code>Here is the rake assets:precompile --trace results:
  
      ruby-1.9.2-p320@stacy1 MARKs-MacBook-Air:stacy1 mark$ rake assets:precompile --trace
      ** Invoke assets:precompile (first_time)
  ** Execute assets:precompile
  /Users/mark/.rvm/rubies/ruby-1.9.2-p320/bin/ruby /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/bin/rake assets:precompile:all RAILS_ENV=production RAILS_GROUPS=assets --trace
  ** Invoke assets:precompile:all (first_time)
  ** Execute assets:precompile:all
  ** Invoke assets:precompile:primary (first_time)
  ** Invoke assets:environment (first_time)
  ** Execute assets:environment
  ** Invoke environment (first_time)
  ** Execute environment
  ** Invoke tmp:cache:clear (first_time)
  ** Execute tmp:cache:clear
  ** Execute assets:precompile:primary
  rake aborted!
  undefined method `[]' for nil:NilClass
    (in /Users/mark/Documents/projects/hosting/stacy1/app/assets/stylesheets/application.css.scss)
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-rails-3.2.6/lib/sass/rails/helpers.rb:32:in `resolver'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-rails-3.2.6/lib/sass/rails/helpers.rb:25:in `font_url'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/script/funcall.rb:112:in `_perform'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/script/node.rb:40:in `perform'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/tree/visitors/perform.rb:298:in `visit_prop'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/tree/visitors/base.rb:37:in `visit'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/tree/visitors/perform.rb:100:in `visit'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/tree/visitors/base.rb:53:in `block in visit_children'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/tree/visitors/base.rb:53:in `map'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/tree/visitors/base.rb:53:in `visit_children'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/tree/visitors/perform.rb:109:in `block in visit_children'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/tree/visitors/perform.rb:121:in `with_environment'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/tree/visitors/perform.rb:108:in `visit_children'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/tree/visitors/base.rb:37:in `block in visit'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/tree/visitors/perform.rb:356:in `visit_directive'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/tree/visitors/base.rb:37:in `visit'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/tree/visitors/perform.rb:100:in `visit'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/tree/visitors/base.rb:53:in `block in visit_children'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/tree/visitors/base.rb:53:in `map'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/tree/visitors/base.rb:53:in `visit_children'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/tree/visitors/perform.rb:109:in `block in visit_children'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/tree/visitors/perform.rb:121:in `with_environment'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/tree/visitors/perform.rb:108:in `visit_children'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/tree/visitors/base.rb:37:in `block in visit'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/tree/visitors/perform.rb:128:in `visit_root'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/tree/visitors/base.rb:37:in `visit'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/tree/visitors/perform.rb:100:in `visit'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/tree/visitors/perform.rb:7:in `visit'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/tree/root_node.rb:20:in `render'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/engine.rb:315:in `_render'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-3.2.12/lib/sass/engine.rb:262:in `render'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sass-rails-3.2.6/lib/sass/rails/compressor.rb:12:in `compress'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/actionpack-3.2.13/lib/sprockets/compressors.rb:74:in `compress'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sprockets-2.2.2/lib/sprockets/processing.rb:243:in `block in css_compressor='
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sprockets-2.2.2/lib/sprockets/processor.rb:29:in `call'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sprockets-2.2.2/lib/sprockets/processor.rb:29:in `evaluate'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/tilt-1.4.1/lib/tilt/template.rb:103:in `render'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sprockets-2.2.2/lib/sprockets/context.rb:193:in `block in evaluate'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sprockets-2.2.2/lib/sprockets/context.rb:190:in `each'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sprockets-2.2.2/lib/sprockets/context.rb:190:in `evaluate'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sprockets-2.2.2/lib/sprockets/bundled_asset.rb:26:in `initialize'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sprockets-2.2.2/lib/sprockets/base.rb:252:in `new'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sprockets-2.2.2/lib/sprockets/base.rb:252:in `build_asset'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sprockets-2.2.2/lib/sprockets/index.rb:93:in `block in build_asset'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sprockets-2.2.2/lib/sprockets/caching.rb:19:in `cache_asset'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sprockets-2.2.2/lib/sprockets/index.rb:92:in `build_asset'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sprockets-2.2.2/lib/sprockets/base.rb:169:in `find_asset'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sprockets-2.2.2/lib/sprockets/index.rb:60:in `find_asset'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/actionpack-3.2.13/lib/sprockets/static_compiler.rb:19:in `block in compile'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sprockets-2.2.2/lib/sprockets/base.rb:219:in `block in each_logical_path'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sprockets-2.2.2/lib/sprockets/base.rb:206:in `block (2 levels) in each_file'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sprockets-2.2.2/lib/sprockets/base.rb:196:in `each'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sprockets-2.2.2/lib/sprockets/base.rb:196:in `each_entry'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sprockets-2.2.2/lib/sprockets/base.rb:204:in `block in each_file'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sprockets-2.2.2/lib/sprockets/base.rb:203:in `each'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sprockets-2.2.2/lib/sprockets/base.rb:203:in `each_file'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/sprockets-2.2.2/lib/sprockets/base.rb:217:in `each_logical_path'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/actionpack-3.2.13/lib/sprockets/static_compiler.rb:18:in `compile'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/actionpack-3.2.13/lib/sprockets/assets.rake:56:in `internal_precompile'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/actionpack-3.2.13/lib/sprockets/assets.rake:70:in `block (3 levels) in &lt;top (required)&gt;'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/task.rb:236:in `call'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/task.rb:236:in `block in execute'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/task.rb:231:in `each'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/task.rb:231:in `execute'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/task.rb:175:in `block in invoke_with_call_chain'
  /Users/mark/.rvm/rubies/ruby-1.9.2-p320/lib/ruby/1.9.1/monitor.rb:201:in `mon_synchronize'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/task.rb:168:in `invoke_with_call_chain'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/task.rb:161:in `invoke'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/actionpack-3.2.13/lib/sprockets/assets.rake:60:in `block (3 levels) in &lt;top (required)&gt;'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/task.rb:236:in `call'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/task.rb:236:in `block in execute'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/task.rb:231:in `each'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/task.rb:231:in `execute'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/task.rb:175:in `block in invoke_with_call_chain'
  /Users/mark/.rvm/rubies/ruby-1.9.2-p320/lib/ruby/1.9.1/monitor.rb:201:in `mon_synchronize'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/task.rb:168:in `invoke_with_call_chain'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/task.rb:161:in `invoke'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/application.rb:149:in `invoke_task'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/application.rb:106:in `block (2 levels) in top_level'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/application.rb:106:in `each'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/application.rb:106:in `block in top_level'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/application.rb:115:in `run_with_threads'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/application.rb:100:in `top_level'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/application.rb:78:in `block in run'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/application.rb:165:in `standard_exception_handling'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/application.rb:75:in `run'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/bin/rake:33:in `&lt;top (required)&gt;'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/bin/rake:23:in `load'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/bin/rake:23:in `&lt;main&gt;'
  Tasks: TOP =&gt; assets:precompile:primary
  rake aborted!
  Command failed with status (1): [/Users/mark/.rvm/rubies/ruby-1.9.2-p...]
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/file_utils.rb:55:in `block in create_shell_runner'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/file_utils.rb:45:in `call'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/file_utils.rb:45:in `sh'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/file_utils_ext.rb:37:in `sh'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/file_utils.rb:82:in `ruby'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/file_utils_ext.rb:37:in `ruby'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/actionpack-3.2.13/lib/sprockets/assets.rake:12:in `ruby_rake_task'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/actionpack-3.2.13/lib/sprockets/assets.rake:21:in `invoke_or_reboot_rake_task'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/actionpack-3.2.13/lib/sprockets/assets.rake:29:in `block (2 levels) in &lt;top (required)&gt;'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/task.rb:236:in `call'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/task.rb:236:in `block in execute'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/task.rb:231:in `each'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/task.rb:231:in `execute'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/task.rb:175:in `block in invoke_with_call_chain'
  /Users/mark/.rvm/rubies/ruby-1.9.2-p320/lib/ruby/1.9.1/monitor.rb:201:in `mon_synchronize'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/task.rb:168:in `invoke_with_call_chain'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/task.rb:161:in `invoke'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/application.rb:149:in `invoke_task'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/application.rb:106:in `block (2 levels) in top_level'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/application.rb:106:in `each'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/application.rb:106:in `block in top_level'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/application.rb:115:in `run_with_threads'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/application.rb:100:in `top_level'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/application.rb:78:in `block in run'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/application.rb:165:in `standard_exception_handling'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/lib/rake/application.rb:75:in `run'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/gems/rake-10.1.0/bin/rake:33:in `&lt;top (required)&gt;'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/bin/rake:23:in `load'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/bin/rake:23:in `&lt;main&gt;'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/bin/ruby_executable_hooks:15:in `eval'
  /Users/mark/.rvm/gems/ruby-1.9.2-p320@stacy1/bin/ruby_executable_hooks:15:in `&lt;main&gt;'
  Tasks: TOP =&gt; assets:precompile`enter code here`
  </code></pre>
  
  <p>Here is the application.css.scss file: </p>
  
  <pre><code> /*
   *= require_self
   *= require_tree .
   */
  </code></pre>