Unable to invoke the before_save callback for each user in console in rails

I am following the Micheal Hartl tutorial on Ruby on Rails. The user created before developing the signin function need to be assigned a remember token. For that I use the following code in console : User.all.each { |user| user.save(validate: false) } Since I have : before save :create remember token in app/models/user.rb, This should create a remember token, but I get the following error on running this : NameError: undefined local variable or method base64' for #<User:0x00559aefda7f20> from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activemodel-4.2.4/lib/active_model/attribute_methods.rb:433:inmethod_missing' from /home/shivani/myapp/app/models/user.rb:13:in create_remember_token' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/callbacks.rb:432:inblock in make_lambda' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/callbacks.rb:164:in call' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/callbacks.rb:164:inblock in halting' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/callbacks.rb:504:in call' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/callbacks.rb:504:inblock in call' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/callbacks.rb:504:in each' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/callbacks.rb:504:incall' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/callbacks.rb:92:in __run_callbacks__' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/callbacks.rb:778:in_run_save_callbacks' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/callbacks.rb:302:in create_or_update' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/persistence.rb:120:insave' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/validations.rb:37:in save' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/attribute_methods/dirty.rb:21:insave' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activerecord-4.2.4/lib/active_record/transactions.rb:286:in block (2 levels) in save' ... 14 levels... from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/railties-4.2.4/lib/rails/commands/console.rb:9:instart' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/railties-4.2.4/lib/rails/commands/commands_tasks.rb:68:in console' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/railties-4.2.4/lib/rails/commands/commands_tasks.rb:39:inrun_command!' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/railties-4.2.4/lib/rails/commands.rb:17:in <top (required)>' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/dependencies.rb:274:inrequire' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/dependencies.rb:274:in block in require' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/dependencies.rb:240:inload_dependency' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/dependencies.rb:274:in require' from /home/shivani/myapp/bin/rails:9:in' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/dependencies.rb:268:in load' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/dependencies.rb:268:inblock in load' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/dependencies.rb:240:in load_dependency' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/gems/2.2.0/gems/activesupport-4.2.4/lib/active_support/dependencies.rb:268:inload' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/2.2.0/rubygems/core_ext/kernel_require.rb:54:in require' from /home/shivani/.rbenv/versions/2.2.3/lib/ruby/2.2.0/rubygems/core_ext/kernel_require.rb:54:inrequire'

Please help!