[Alumnionrails-errors] [ALI] courses#upload_picture (NoMethodError) "undefined method `[]' for nil:NilClass"

[Application Error]

A NoMethodError occurred in courses#upload_picture:

  undefined method `[]' for nil:NilClass
  [RAILS_ROOT]/app/controllers/courses_controller.rb:93:in `upload_picture'

-------------------------------
Request:
-------------------------------

  * URL       : http://beta.alumnionrails.com/courses/upload_picture
  * IP address: 66.249.66.11
  * Parameters: {"action"=>"upload_picture", "controller"=>"courses"}
  * Rails root: /home/www/beta.alumnionrails.com/rails/releases/20100319115321

-------------------------------
Session:
-------------------------------

  * session id: "a9e24d5812c0f12f3b0c2cb57cd068d7"
  * data: {"flash"=>{}}

-------------------------------
Environment:
-------------------------------

  * GATEWAY_INTERFACE      : CGI/1.2
  
  * HTTP_ACCEPT            : */*
  
  * HTTP_ACCEPT_ENCODING   : gzip,deflate
  
  * HTTP_CONNECTION        : Keep-Alive
  
  * HTTP_FROM              : googlebot(at)googlebot.com
  
  * HTTP_HOST              : 127.0.0.1:8071
  
  * HTTP_USER_AGENT        : Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)
  
  * HTTP_VERSION           : HTTP/1.1
  
  * HTTP_X_FORWARDED_FOR   : 66.249.66.11
  
  * HTTP_X_FORWARDED_HOST  : beta.alumnionrails.com
  
  * HTTP_X_FORWARDED_SERVER: beta.alumnionrails.com
  
  * PATH_INFO              : /courses/upload_picture
  
  * REMOTE_ADDR            : 127.0.0.1
  
  * REQUEST_METHOD         : GET
  
  * REQUEST_PATH           : /courses/upload_picture
  
  * REQUEST_URI            : /courses/upload_picture
  
  * SCRIPT_NAME            : /
  
  * SERVER_NAME            : 127.0.0.1
  
  * SERVER_PORT            : 8071
  
  * SERVER_PROTOCOL        : HTTP/1.1
  
  * SERVER_SOFTWARE        : Mongrel 1.1.5
  
  
  * Process: 8699
  * Server : s15280848

-------------------------------
Backtrace:
-------------------------------

  [RAILS_ROOT]/app/controllers/courses_controller.rb:93:in `upload_picture'
  /usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/base.rb:1162:in `send'
  /usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/base.rb:1162:in `perform_action_without_filters'
  /usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/filters.rb:580:in `call_filters'
  /usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/filters.rb:573:in `perform_action_without_benchmark'
  /usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/benchmarking.rb:68:in `perform_action_without_rescue'
  /usr/local/lib/ruby/1.8/benchmark.rb:293:in `measure'
  /usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/benchmarking.rb:68:in `perform_action_without_rescue'
  /usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/rescue.rb:201:in `perform_action_without_caching'
  /usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/caching/sql_cache.rb:13:in `perform_action'
  /usr/local/lib/ruby/gems/1.8/gems/activerecord-2.1.0/lib/active_record/connection_adapters/abstract/query_cache.rb:33:in `cache'
  /usr/local/lib/ruby/gems/1.8/gems/activerecord-2.1.0/lib/active_record/query_cache.rb:8:in `cache'
  /usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/caching/sql_cache.rb:12:in `perform_action'
  /usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/base.rb:529:in `send'
  /usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/base.rb:529:in `process_without_filters'
  /usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/filters.rb:569:in `process_without_session_management_support'
  /usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/session_management.rb:130:in `process'
  /usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/base.rb:389:in `process'
  /usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/dispatcher.rb:149:in `handle_request'
  /usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/dispatcher.rb:107:in `dispatch'
  /usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/dispatcher.rb:104:in `synchronize'
  /usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/dispatcher.rb:104:in `dispatch'
  /usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/dispatcher.rb:120:in `dispatch_cgi'
  /usr/local/lib/ruby/gems/1.8/gems/actionpack-2.1.0/lib/action_controller/dispatcher.rb:35:in `dispatch'
  /usr/local/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel/rails.rb:76:in `process'
  /usr/local/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel/rails.rb:74:in `synchronize'
  /usr/local/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel/rails.rb:74:in `process'
  /usr/local/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:159:in `process_client'
  /usr/local/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:158:in `each'
  /usr/local/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:158:in `process_client'
  /usr/local/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:285:in `run'
  /usr/local/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:285:in `initialize'
  /usr/local/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:285:in `new'
  /usr/local/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:285:in `run'
  /usr/local/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:268:in `initialize'
  /usr/local/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:268:in `new'
  /usr/local/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel.rb:268:in `run'
  /usr/local/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel/configurator.rb:282:in `run'
  /usr/local/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel/configurator.rb:281:in `each'
  /usr/local/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel/configurator.rb:281:in `run'
  /usr/local/lib/ruby/gems/1.8/gems/mongrel-1.1.5/bin/mongrel_rails:128:in `run'
  /usr/local/lib/ruby/gems/1.8/gems/mongrel-1.1.5/lib/mongrel/command.rb:212:in `run'
  /usr/local/lib/ruby/gems/1.8/gems/mongrel-1.1.5/bin/mongrel_rails:281
  /usr/local/bin/mongrel_rails:19:in `load'
  /usr/local/bin/mongrel_rails:19