Move Null type to the Bottom in the VM (fixes #28025).

runtime/vm/dart_api_impl_test.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "bin/builtin.h"
 #include "vm/compiler.h"
 #include "include/dart_api.h"
 #include "include/dart_mirrors_api.h"
 #include "include/dart_native_api.h"
 #include "include/dart_tools_api.h"
@@ skipping 989 matching lines @@
   Dart_Handle below_min = Dart_NewIntegerFromHexCString("-1");
   EXPECT(Dart_IsInteger(below_min));
   fits = true;
   result = Dart_IntegerFitsIntoUint64(below_min, &fits);
   EXPECT_VALID(result);
   EXPECT(!fits);
 }
 
 
 TEST_CASE(ArrayValues) {
+  EXPECT(!Dart_IsList(Dart_Null()));
   const int kArrayLength = 10;
   Dart_Handle str = NewString("test");
   EXPECT(!Dart_IsList(str));
   Dart_Handle val = Dart_NewList(kArrayLength);
   EXPECT(Dart_IsList(val));
   intptr_t len = 0;
   Dart_Handle result = Dart_ListLength(val, &len);
   EXPECT_VALID(result);
   EXPECT_EQ(kArrayLength, len);
 
@@ skipping 446 matching lines @@
   EXPECT(Dart_IsError(result));
   EXPECT(Dart_IsUnhandledExceptionError(result));
 
   result = Dart_ListSetAt(list_access_test_obj, 0, Dart_NewInteger(42));
   EXPECT(Dart_IsError(result));
   EXPECT(Dart_IsUnhandledExceptionError(result));
 }
 
 
 TEST_CASE(MapAccess) {
+  EXPECT(!Dart_IsMap(Dart_Null()));
   const char* kScriptChars =
       "Map testMain() {"
       "  return {"
       "    'a' : 1,"
       "    'b' : null,"
       "  };"
       "}";
   Dart_Handle result;
 
   // Create a test library and Load up a test script in it.
@@ skipping 8421 matching lines @@
   EXPECT_VALID(result);
   result = Dart_FinalizeLoading(false);
   EXPECT_VALID(result);
   result = Dart_Invoke(lib, NewString("foozoo"), 0, NULL);
   EXPECT(Dart_IsError(result));
 }
 
 #endif  // !PRODUCT
 
 }  // namespace dart