Provide listOfNotNull method.

libraries/stdlib/test/collections/CollectionTest.kt

@@ -47,6 +47,18 @@ class CollectionTest {
         }
     }
 
+    test fun listOfNotNull() {
+        val l1: List<Int> = listOfNotNull(null)
+        assertTrue(l1.isEmpty())
+
+        val s: String? = "value"
+        val l2: List<String> = listOfNotNull(s)
+        assertEquals(s, l2.single())
+
+        val l3: List<String> = listOfNotNull("value1", null, "value2")
+        assertEquals(listOf("value1", "value2"), l3)
+    }
+
     test fun filterIntoSet() {
         val data = listOf("foo", "bar")
         val foo = data.filterTo(hashSetOf<String>()) { it.startsWith("f") }