title: How to display error message on model in rails
body: <p>I need to display error message on model in rails,</p>
  
  <p>my coding on model is like this,</p>
  
  <pre><code>if my_address.valid?
    # I need here the validation error.
     return nil
  end
  </code></pre>
  
  <p>I used errors.add("Invalid address") but it is not working </p>
  
  <p>please help to solve this problem ,</p>