SI-9377 ScalaVersion init no longer fails if versionless

If the version string was empty, ScalaVersion would
indignantly refuse to initialize. Now it takes a missing
property as "none".

Author: som-snytt

src/compiler/scala/tools/nsc/settings/ScalaVersion.scala

@@ -97,6 +97,7 @@ object ScalaVersion {
 
     versionString match {
       case "none" => NoScalaVersion
+      case ""     => NoScalaVersion
       case "any"  => AnyScalaVersion
       case vpat(majorS, minorS, revS, buildS) =>
         SpecificScalaVersion(toInt(majorS), toInt(minorS), toInt(revS), toBuild(buildS))

test/junit/scala/tools/nsc/settings/ScalaVersionTest.scala

@@ -57,4 +57,9 @@ class ScalaVersionTest {
     assertThrows[NumberFormatException] { ScalaVersion("2-.") } // scalacheck territory
     assertThrows[NumberFormatException] { ScalaVersion("any.7") }
   }
+
+  // SI-9377
+  @Test def `missing version is as good as none`() {
+    assertEquals(NoScalaVersion, ScalaVersion(""))
+  }
 }