title: scala - map.get returns None for null key but not for null value
body: <p>Is there any better way to do following?</p>
  
  <pre><code>val v = map.get(key)
        v match {
          case None =&gt; default
          case Some(str) =&gt; {
            if(str == null) default else str &lt;&lt; how to avoid additional null check here
          }
        }
  </code></pre>