don't try to cast 'None' into a C++ lvalue reference
diff --git a/example/issues.ref b/example/issues.ref
index 13bafc2..2d34f42 100644
--- a/example/issues.ref
+++ b/example/issues.ref
@@ -5,3 +5,6 @@
 [Placeholder[1], Placeholder[2], Placeholder[3], Placeholder[4]]
 [3, 5, 7, 9, 11, 13, 15]
 0==0, 1==1, 2==2, 3==3, 4==4, 5==5, 6==6, 7==7, 8==8, 9==9, 
+Failed as expected: Incompatible function arguments. The following argument types are supported:
+    1. (example.issues.ElementA) -> NoneType
+