user adds public key failed

I, [2015-03-25T18:28:28.954105 #20997]  INFO -- : Started PATCH "/u/test02hkwtf" for 127.0.0.1 at 2015-03-25 18:28:28 +0800
I, [2015-03-25T18:28:28.956038 #20997]  INFO -- : Processing by UsersController#update as HTML
I, [2015-03-25T18:28:28.956121 #20997]  INFO -- :   Parameters: {"utf8"=>"✓", "authenticity_token"=>"Vz1pHCvKdy3HpuY6q5EMyGtF8H/a3fRZqcaURKKLqx0=", "user"=>{"profile_attributes"=>{"public_keys"=>"ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDRuZYm2nsXUJ8PMpPHuNWqxY/qZurZB7kPARoOSVfCZdZ8wwP2MRW8xhF+bokSO0AiO1nROXDe9dRQHSgHmGlT9SbkhcdrSbsOxsrMcDZiTUY0dao+5mT4AZP+RuOYD1kHr6sG0PWb4nlWzd+Cg5SvOv9Kv4JyChsmxqBj/Ck0oWtw7wQkOsp/RMxYHm76+PWe45JJqbgWA0MT8/Z85dKwZN660UUYCmXJWlDvIHWSIPhmNHpXmY9FnjLEYkvyOL8VXTmzjMumVr3adpghYYmOiasVFIW8MGEdRts7ibn68eskopklC2wlY368zc936ApexPscHkh7Ez1+UFWCrAHn jimmychu@JC-MBP.local", "id"=>"2"}}, "commit"=>"更新", "id"=>"test02hkwtf"}
I, [2015-03-25T18:28:28.963227 #20997]  INFO -- : Completed 500 Internal Server Error in 7ms
F, [2015-03-25T18:28:28.966577 #20997] FATAL -- : 
NameError (undefined local variable or method `public_keys' for #<Class:0x007f9107a197e0>):
  app/models/profile.rb:20:in `block in <class:Profile>'
  app/controllers/users_controller.rb:8:in `update'
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