Add a run test

Author: noti0na1

tests/explicit-nulls/run/from-nullable.check

@@ -0,0 +1,2 @@
+hello
+None

tests/explicit-nulls/run/from-nullable.scala

@@ -0,0 +1,17 @@
+object Test:
+  import scala.annotation.experimental
+
+  @experimental def main(args: Array[String]): Unit =
+    val s1: String | Null = "hello"
+    val s2: String | Null = null
+
+    val opts1: Option[String] = Option.fromNullable(s1)
+    val opts2: Option[String] = Option.fromNullable(s2)
+
+    opts1 match
+      case Some(s) => println(s)
+      case None => println("None")
+
+    opts2 match
+      case Some(s) => println(s)
+      case None => println("None")