title: Firestore - Check if the document which is being updated exists
body: <p>As far as I know - In order to check whether a <code>document</code> exists or not, I should use the <code>get</code> function and see if it does. </p>
  
  <p><strong>My question is about checking while updating - Is it possible?</strong> (Considering that the <code>document</code> might be gone when the update occurs).</p>
  
  <p>I have tried to update an empty <code>document</code> and I got an error which says that the document doesn't exist, but I think this might not be the successful way to check this.</p>