title: password_digest error
body: <p>i use omniauth-identity for authentication on my project. i lso use mongodb for database.my identity model is like below:</p>
  
  <pre><code>class Identity
    include Mongoid::Document
    include OmniAuth::Identity::Models::Mongoid
  
    field :name, type: String
    field :email, type: String
    field :password_digest, type: String
  
    validates_presence_of :name
    validates_uniqueness_of :email
    validates_format_of :email, :with =&gt; /^[-a-z0-9_+\.]+\@([-a-z0-9]+\.)+[a-z0-9]{2,4}$/i
  end
  </code></pre>
  
  <p>my identities controller is like below:</p>
  
  <pre><code>class IdentitiesController &lt; ApplicationController
  
    def new 
     @identity = env['omniauth.identity']
    end
  
  end
  </code></pre>
  
  <p>i run project. i don't fill in texts. it gives me error</p>
  
  <pre><code>Password digest can't be blank
  Name can't be blank
  Email is invalid
  </code></pre>
  
  <p>problem is here that, <code>Password digest can't be blank</code> warning. it must not be an error. How can i solve this?</p>