title: Ransack OR queries
body: <p>I want to make a search for all fields that are NULL or have the value of -1 using ransack.</p>
  
  <pre><code>search({:param_name_null =&gt; 1 }) 
  </code></pre>
  
  <p>will give the nulls</p>
  
  <pre><code>search({:param_name_is_any =&gt; -1 })
  </code></pre>
  
  <p>will give the -1s</p>
  
  <p>How do i make an OR between these two using ransack?
  Thanks</p>