Devise update user without password

I want to update users attributes without password in devise. The case is like, if password and password confirmation fields are not blank then I need devise error and if they are blank then other user attributes need to be updated. How could I do this with devise? Thanks in advance!

[sessan]

ユーザーが入力したパスワードなしで、deviseのユーザーモデルの属性を更新する方法。