How to use the botbuilder-azure.DocumentDbClient function in botbuilder-azure

var userName = session.userData[UserNameKey];
    if (!userName) {
        return session.beginDialog('greet');
    }

    // has the user been welcomed to the conversation?
    if (!session.privateConversationData[UserWelcomedKey]) {
        session.privateConversationData[UserWelcomedKey] = true;
        return session.send('Welcome back %s! Remember the rules: %s', userName, HelpMessage);
    }

    session.beginDialog('search');
}).set('storage', inMemoryStorage); // Register in memory storage

// Azure DocumentDb State Store
var docDbClient = new azure.DocumentDbClient({
    host: process.env.DOCUMENT_DB_HOST,
    masterKey: process.env.DOCUMENT_DB_MASTER_KEY,
    database: process.env.DOCUMENT_DB_DATABASE,
    collection: process.env.DOCUMENT_DB_COLLECTION
});
var botStorage = new azure.AzureBotStorage({ gzipData: false }, docDbClient);

// Set Custom Store
bot.set('storage', botStorage);

// Enable Conversation Data persistence
bot.set('persistConversationData', true);

// search dialog
bot.dialog('search', function (session, args, next) {
    // perform search