title: Custom function doesn't work with ArrayFormula
body: <p>i followed the post
  <a href="https://developers.google.com/apps-script/guides/sheets/functions" rel="nofollow noreferrer">https://developers.google.com/apps-script/guides/sheets/functions</a></p>
  
  <pre><code>function DOUBLE(input) {
      return input * 2;
  }
  </code></pre>
  
  <p>and copied the very simple DOUBLE function into my app-script.</p>
  
  <pre><code>=double(A1)
  </code></pre>
  
  <p>is working and double my integer in 'A1'
  But when i filled column A with values, like</p>
  
  <pre><code>A1 = 2
  A2 = 3
  A3 = 4
  ....
  </code></pre>
  
  <p>And in B1 cell, i run </p>
  
  <pre><code>=arrayformula(double(A1:A))
  </code></pre>
  
  <p>it returned error "Result was not a number", #NUM!</p>
  
  <p>I am not sure what goes wrong. Could any app-script gurus helps?</p>
  
  <p>Thanks</p>