Check in codegen test expectations.

test/codegen/expect/language/main_test_41_multi.js

+dart_library.library('language/main_test_41_multi', null, /* Imports */[
+  'dart_sdk'
+], function load__main_test_41_multi(exports, dart_sdk) {
+  'use strict';
+  const core = dart_sdk.core;
+  const dart = dart_sdk.dart;
+  const dartx = dart_sdk.dartx;
+  const main_test_41_multi = Object.create(null);
+  let __Todynamic = () => (__Todynamic = dart.constFn(dart.definiteFunctionType(dart.dynamic, [], {a: dart.dynamic})))();
+  main_test_41_multi.main = function(opts) {
+    let a = opts && 'a' in opts ? opts.a : null;
+  };
+  dart.fn(main_test_41_multi.main, __Todynamic());
+  // Exports:
+  exports.main_test_41_multi = main_test_41_multi;
+});