title: Why can't I match on a Seq.empty?
body: <p>I tried matching a seq like this:</p>
  
  <pre><code>val users: Seq[User] = ....
  
  users match {
    case Seq.empty =&gt; ....
    case ..
  }
  </code></pre>
  
  <p>I got an error saying:</p>
  
  <pre><code>stable identifier required, but scala.this.Predef.Set.empty found.
  </code></pre>
  
  <p>Can someone explain why I can't do this? i.e. the theory behind it</p>