title: Strange usage of in_array
body: <p>I stumbled upon this code:</p>
  
  <pre><code>in_array(($_GET['some_value']??-1),[])
  </code></pre>
  
  <p>and I'm having some trouble understanding it. My questions are as follows:</p>
  
  <ol>
  <li>What does the <code>??</code> operator mean in this context? My experience tells me it's similar to null coalescing but I'm not sure.</li>
  <li>What does <code>in_array</code> do if <code>haystack</code> is an empty array? Again, seems like it would always return <code>FALSE</code> but I'm new to PHP so I'd like confirmation on this.</li>
  </ol>