The null tests that I added for Dart_NewString{8,16,32} were too restrictive.

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 "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/json.h"
 #include "platform/utils.h"
 #include "vm/class_finalizer.h"
 #include "vm/dart_api_impl.h"
@@ skipping 6499 matching lines @@
                "expects argument 'length' to be in the range");
   EXPECT_ERROR(Dart_NewString16(chars16, TwoByteString::kMaxElements+1),
                "expects argument 'length' to be in the range");
   EXPECT_ERROR(Dart_NewString32(chars32, -1),
                "expects argument 'length' to be in the range");
   EXPECT_ERROR(Dart_NewString32(chars32, FourByteString::kMaxElements+1),
                "expects argument 'length' to be in the range");
 }
 
 
+TEST_CASE(NewString_Null) {
+  Dart_Handle str = Dart_NewString8(NULL, 0);
+  EXPECT_VALID(str);
+  EXPECT(Dart_IsString(str));
+  intptr_t len = -1;
+  EXPECT_VALID(Dart_StringLength(str, &len));
+  EXPECT_EQ(0, len);
+
+  str = Dart_NewString16(NULL, 0);
+  EXPECT_VALID(str);
+  EXPECT(Dart_IsString(str));
+  len = -1;
+  EXPECT_VALID(Dart_StringLength(str, &len));
+  EXPECT_EQ(0, len);
+
+  str = Dart_NewString32(NULL, 0);
+  EXPECT_VALID(str);
+  EXPECT(Dart_IsString(str));
+  len = -1;
+  EXPECT_VALID(Dart_StringLength(str, &len));
+  EXPECT_EQ(0, len);
+}
+
+
 #endif  // defined(TARGET_ARCH_IA32) || defined(TARGET_ARCH_X64).
 
 }  // namespace dart