For reasons beyond logic, null matches any exception type.

dart/frog/leg/ssa/builder.dart

Index: dart/frog/leg/ssa/builder.dart
diff --git a/dart/frog/leg/ssa/builder.dart b/dart/frog/leg/ssa/builder.dart
index cffadd05bb0aadf001ff35a9b91f42ff966648c9..9db538b274b2a99adeeb0344025f2d09cbd55fff 100644
--- a/dart/frog/leg/ssa/builder.dart
+++ b/dart/frog/leg/ssa/builder.dart
@@ -2298,7 +2298,7 @@ class SsaBuilder implements Visitor {
           if (typeElement == null) {
             compiler.cancel('Catch with unresolved type', node: catchBlock);
           }
-          condition = new HIs(typeElement, unwrappedException);
+          condition = new HIs(typeElement, unwrappedException, nullOk: true);
           push(condition);
         }
       }