Json::CharReaderBuilder builder;
builder.settings_["allowDroppedNullPlaceholders"] = true;
std::auto_ptr<Json::CharReader> reader(builder.newCharReader());

Json::StreamWriterBuilder writer;

Json::Value root;
std::string rawJson = "{'key': \"qwerty:123456\", 'isError':  false }";
std::string errors;

if (reader->parse(rawJson.c_str(), rawJson.c_str() + rawJson.length(), &root, &errors))
{
    std::cout << Json::writeString(writer, root) << std::endl;
}
else
{
    std::cout << errors << std::endl;
}