title: ArgumentError: You need to supply at least one validation with :if
body: <p>I have a simple model</p>
  
  <pre><code>class Task &lt; ActiveRecord::Base
    validates :deadline, :if =&gt; :deadline_in_future?
  
    def deadline_in_future?
      Date.today &lt; self.deadline
    end
  end
  </code></pre>
  
  <p>All seems ok, but when I in my rails console</p>
  
  <pre><code>irb(main):001:0&gt; Task.new
  ArgumentError: You need to supply at least one validation
  </code></pre>
  
  <p>Where is the problem?</p>