title: In Scala return value itself for default pattern matching
body: <p>For <code>value: Any</code> I need to check one string case.<br />
  For rest cases should return <code>value</code> itself.<br />
  What is the right syntax: <code>case _ =&gt; _ ?</code></p>
  
  <pre><code>def foo(value: Any) = value match {
    case x: String =&gt; if (x == "cond") None else x
    case _ =&gt; _ // Compiler -&gt; Not found value x$1. Unbound placeholder parameter
  }
  </code></pre>