cleaner workaround for #7882

Author: olhotak

library/src/scala/runtime/Scala3RunTime.scala

@@ -15,8 +15,7 @@ object Scala3RunTime:
    *  Extracted to minimize the bytecode size at call site.
    */
   def nn[T](x: T | Null): x.type & T =
-    val isNull = x == null
-    if (isNull) throw new NullPointerException("tried to cast away nullability, but value is null")
-    else x.asInstanceOf[x.type & T]
+    if (x == null) throw new NullPointerException("tried to cast away nullability, but value is null")
+    else x
 
 end Scala3RunTime