title: How to check if an array in a firestore document is empty?
body: <p>I'm building out an app in flutter and I want to run a query to determine if the array in my firestore document is empty. Is there a way to do this? </p>
  
  <p>Here is a picture of my data structured in firestore. </p>
  
  <p><a href="https://i.stack.imgur.com/icLU2.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/icLU2.png" alt="enter image description here"></a></p>
  
  <p>I know there is an <strong>arrayContains method</strong> but I'm not sure on how to check for an <strong>empty array</strong>. Here is my current code. </p>
  
  <pre><code>_postsStream = await _firestore
          .collectionGroup('posts')
          .where('timestamp', isGreaterThanOrEqualTo: _start)
          .where('timestamp', isLessThanOrEqualTo: _end)
          .where('problems', arrayContains: )
          .snapshots();
  </code></pre>
  
  <p>I left the arrayContains: intentionally empty for now. Please advise on how I would go about implementing this feature. Thanks in advance! </p>