title: Scala companion class warning
body: <p>I am new to Scala programming, can someone explain me below warning reason? </p>
  
  <p><img src="https://i.stack.imgur.com/z2gGc.png" alt="Scala-Companion-Warning">
  I tried to find the reason and it seems like a big fixed earlier: <a href="https://issues.scala-lang.org/browse/SI-6439" rel="noreferrer">https://issues.scala-lang.org/browse/SI-6439</a></p>
  
  <p>So why I am getting this warning?</p>