update_attributes() Error

Follow the book Agile Web Development with Rails, copy the depot's Model
User.

And my Users table has another two fields, address and email.

When I tried to update these two fields, the code like

user = User.find(1)
user.update_attributes!(:address => "abc", :email => "abc@hot.com")

then gave me an error: Validation failed: Password can't be blank

but I don't wanna update the password, how can I solve the problem?
Thanks!