title: How to make where condition include nil value
body: <p>I find ActiveRecord, funnel value is not "input" value</p>
  
  <p>and I make <b> where condition</b></p>
  
  <p>here is my code</p>
  
  <pre><code>@calls = Call.searchable.where.not(funnel: "input") 
  </code></pre>
  
  <p>these command work good, but result is also except nil value</p>
  
  <p>I wanna only <b> funnel is not 'input' </b></p>
  
  <p>how to add OR condition in where statement</p>
  
  <p>SQL Statement is </p>
  
  <pre><code>select * from call where is_visible = 1 and (funnel != 'input or funnel is null)
  </code></pre>