title: Why update_attribute firing validation?
body: <p>I have two disabled textbox. And it's passing nil as value.</p>
  
  <p>Still update_attribute is firing validation for those textboxes. </p>
  
  <p>As per my knowledge update_attribute should not update the spefic column which has nil value passed.</p>
  
  <pre><code>validates_inclusion_of :text_response_time, :in =&gt; 0..60, :message =&gt; " should be between 0 to 60 minutes."
  
  (rdb:589) params[:test][:text_response_time]
  nil
  (rdb:589) @test.update_attributes!(params[:test])
  ActiveRecord::RecordInvalid Exception: Validation failed: Text response time  should be between 0 to 60 minutes.
  </code></pre>
  
  <p>Any Idea!</p>