anchor.diff:    Db._authDb(this.databaseName);
     ServerConfig _parseUri(String uriString) {
       var uri = Uri.parse(uriString);
  +
       if (uri.scheme != 'mongodb') {
         throw new MongoDartError(
             'Invalid scheme in uri: $uriString ${uri.scheme}');
       }
  +
       var serverConfig = new ServerConfig();
       serverConfig.host = uri.host;
       serverConfig.port = uri.port;
  +
       if (serverConfig.port == null || serverConfig.port == 0) {
  -      serverConfig.port = 27017;
  -    }
  -    if (uri.userInfo != '') {
  +      serverConfig.port = MONGO_DEFAULT_PORT;
  +    }
  +
  +    if (uri.userInfo.isNotEmpty) {
         var userInfo = uri.userInfo.split(':');
  +
         if (userInfo.length != 2) {
           throw new MongoDartError(
               'Invalid format of userInfo field: $uri.userInfo');
         }
  +
         serverConfig.userName = userInfo[0];
         serverConfig.password = userInfo[1];
       }
  -    if (uri.path != '') {
  +
  +    if (uri.path.isNotEmpty) {
         databaseName = uri.path.replaceAll('/', '');
       }
   
  -    uri.queryParameters.forEach((String k, String v) {
  -      if (k == _UriParameters.authMechanism) {
  -        selectAuthenticationMechanism(v);
  -      }
  -      if (k == _UriParameters.authSource) {
  -        authSourceDb = new Db._authDb(v);
  +    uri.queryParameters.forEach((String queryParam, String value) {
  +      if (queryParam == _UriParameters.authMechanism) {
  +        selectAuthenticationMechanism(value);
  +      }
  +
  +      if (queryParam == _UriParameters.authSource) {
  +        authSourceDb = new Db._authDb(value);
         }
       });
   
       return serverConfig;
     }
   
  -  void selectAuthenticationMechanism(String v) {
  -    if (v == ScramSha1Authenticator.name) {
  +  void selectAuthenticationMechanism(String authenticationSchemeName) {
  +    if (authenticationSchemeName == ScramSha1Authenticator.name) {
         _authenticationScheme = AuthenticationScheme.SCRAM_SHA_1;
  -    } else if (v == MongoDbCRAuthenticator.name) {
  +    } else if (authenticationSchemeName == MongoDbCRAuthenticator.name) {
         _authenticationScheme = AuthenticationScheme.MONGODB_CR;
       } else {
         throw new MongoDartError(
  -          "Provided authentication scheme is not supported : $v");
  +          "Provided authentication scheme is not supported : $authenticationSchemeName");
       }
     }
   
  
positive.code: }
  
  class Db {
    State state = State.INIT;
    final _log = new Logger('Db');
    String databaseName;
    String _debugInfo;
    Db authSourceDb;
    final List<String> _uriList = new List<String>();
    _ConnectionManager _connectionManager;
    _Connection get _masterConnection => _connectionManager.masterConnection;
    WriteConcern _writeConcern;
  
negative.code:     if (writeConcern == null) {
        writeConcern = _writeConcern;
      }
  
      if (writeConcern == WriteConcern.ERRORS_IGNORED) {
        return new Future.value({'ok': 1.0});
      } else {
  