allow nullable expressions to be used for lazily creating new items if there is not a value in the Map

libraries/stdlib/src/kotlin/Maps.kt

@@ -34,7 +34,7 @@ val <K,V> Map.Entry<K,V>.value : V
  *
  * @includeFunctionBody ../../test/MapTest.kt getOrElse
  */
-public inline fun <K,V> Map<K,V>.getOrElse(key: K, defaultValue: ()-> V) : V {
+public inline fun <K,V> Map<K,V>.getOrElse(key: K, defaultValue: ()-> V?) : V? {
     val current = this.get(key)
     if (current != null) {
         return current

libraries/stdlib/test/CollectionTest.kt

@@ -184,7 +184,7 @@ class CollectionTest {
         assertEquals(4, byLength.size())
 
         val l3 = byLength.getOrElse(3, {ArrayList<String>()})
-        assertEquals(2, l3.size)
+        assertEquals(2, l3?.size)
     }
 
     test fun makeString() {