Ruby on Rails

I have a user model in  which username and email field, i am login with username  when i am creating user i want it's email may be blank, but when i am register user from another model it gives error User email can't be blank.
I already make changes email field in confgi/devise.rb, but it doesn't work.

Here is My User model

class User < ActiveRecord::Base

  has_and_belongs_to_many :roles

  devise :database_authenticatable, :registerable, :rememberable, :token_authenticatable, :trackable,
         :validatable, :timeoutable ,:lockable, :recoverable , :authentication_keys => [:username]

  attr_accessible :email, :username, :password, :password_confirmation, :remember_me, :role_ids, :roles
  validates :email , :presence => false
end
Please, let me know where i am wrong.

Thanks,

Tushar Patil.

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