Fix NSString conversions to treat a null NSString as a string of length 0, in...

base/sys_string_conversions_mac_unittest.mm

+// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import <Foundation/Foundation.h>
+
+#include "base/string16.h"
+#include "base/sys_string_conversions.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+TEST(SysStrings, ConversionsFromNSString) {
+  EXPECT_STREQ("Hello, world!",
+               base::SysNSStringToUTF8(@"Hello, world!").c_str());
+
+  // Conversions should be able to handle a NULL value without crashing.
+  EXPECT_STREQ("", base::SysNSStringToUTF8(nil).c_str());
+  EXPECT_EQ(string16(), base::SysNSStringToUTF16(nil));
+  EXPECT_STREQ(L"", base::SysNSStringToWide(nil).c_str());
+}