title: Devise - could not find valid mapping error while disabling a user
body: <p>Iam trying to disable auser using active_for_authentication? method. 
  My problem is whenever i try to signin with a disabled user, the app throws an error . </p>
  
  <pre><code>RuntimeError (Could not find a valid mapping for #&lt;User details&gt;
  </code></pre>
  
  <p>user.rb</p>
  
  <pre><code>  devise :database_authenticatable, :registerable,:recoverable,
           :rememberable, :trackable, :validatable
  
  def is_active?
    false
  end
  
  def active_for_authentication?
    super &amp;&amp; self.is_active?
  end
  </code></pre>