Assertions when approximating platform types in delegation by expression

compiler/testData/codegen/boxAgainstJava/notNullAssertions/Delegation.java

@@ -0,0 +1,7 @@
+public class Delegation {
+    public static class ReturnNull {
+        public String foo() {
+            return null;
+        }
+    }
+}

compiler/testData/codegen/boxAgainstJava/notNullAssertions/Delegation.kt

@@ -0,0 +1,21 @@
+trait Tr { 
+    fun foo(): String
+}
+
+class DelegateTo : Delegation.ReturnNull(), Tr {
+    override fun foo() = super<Delegation.ReturnNull>.foo()
+}
+
+class DelegateFrom : Tr by DelegateTo() {
+}
+
+fun box(): String {
+    try {
+        DelegateFrom().foo()
+        return "Fail: should have been an exception"
+    }
+    catch(e: IllegalStateException) {
+        println(e.getMessage())
+        return "OK"
+    }
+}