Error:
undefined method `[]' for nil:NilClass
  ./make-gallery.rb:87:in `show_get_size'
  ./make-gallery.rb:92:in `show_color'
  ./make-gallery.rb:115:in `show'
  ./make-gallery.rb:188:in `show'
  /home/masuhara/tmp/is2008-report2-download/g840494/report02.rb:105
  ./make-gallery.rb:131:in `load'
  ./make-gallery.rb:131:in `process_student'
  ./make-gallery.rb:127:in `each'
  ./make-gallery.rb:127:in `process_student'
  ./make-gallery.rb:157:in `process_all_students'
  ./make-gallery.rb:151:in `each'
  ./make-gallery.rb:151:in `process_all_students'
  (irb):13:in `irb_binding'
  /usr/lib/ruby/1.8/irb/workspace.rb:52:in `irb_binding'
  /usr/lib/ruby/1.8/irb/workspace.rb:52
==============================