title: Why is this XQuery return an empty sequence while I'm expecting 5?
body: <p>I'm confused with the below query, I expect the result should be <strong>5</strong> but it returns an <strong>empty sequence</strong>.</p>
  <p><a href="https://i.stack.imgur.com/bKxSc.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/bKxSc.png" alt="enter image description here" /></a></p>
  <pre><code>let $num := 5
  let $num1 := ()
  let $add := $num + $num1
  return $add
  </code></pre>