Error:
undefined method `+' for nil:NilClass
  /home/masuhara/tmp/is2008-report2-download/g840517/report02.rb:187:in `brighter'
  /home/masuhara/tmp/is2008-report2-download/g840517/report02.rb:186:in `each'
  /home/masuhara/tmp/is2008-report2-download/g840517/report02.rb:186:in `brighter'
  /home/masuhara/tmp/is2008-report2-download/g840517/report02.rb:185:in `each'
  /home/masuhara/tmp/is2008-report2-download/g840517/report02.rb:185:in `brighter'
  /home/masuhara/tmp/is2008-report2-download/g840517/report02.rb:212
  ./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
==============================