CosmosDBTrigger: Object reference not set to an instance of an object

When I try to execute newly created azure function with CosmosDBTrigger, I get the above exception for the function with cosmosdb trigger

Investigative information

Environment: Visual Studio 2017 15.3.5

Packages referenced:

• Marvin.JsonPatch.Dynamic Version="1.1.0"
• Microsoft.Azure.DocumentDB Version="1.17.0"
• Microsoft.Azure.WebJobs Version="2.1.0-beta4"
• Microsoft.Azure.WebJobs.Extensions.DocumentDB Version="1.1.0-beta4"
• Microsoft.Azure.WebJobs.ServiceBus Version="2.0.0"
• Microsoft.NET.Sdk.Functions Version="1.0.5"
• Newtonsoft.Json Version="10.0.3"
• System.Configuration.ConfigurationManager Version="4.4.0"

Steps to reproduce the issue

Provide the steps required to reproduce the problem:

• Create a new Azure Function Project from Visual Studio
• Add a function (i didn't find any option for CosmosDB Binding so i created using HttpTrigger) once the .cs file is created, replace the file with the code that i have put below.
• Build
• Hit F5

Here is the code sample

    public static class AddEventInEventStore
    {
        [FunctionName("AddEventInEventStore")]
        public static void Run([CosmosDBTrigger("db", "Items",
            ConnectionStringSetting = "AzureWebJobsDocumentDBConnectionString",
            LeaseCollectionName = "leases", LeaseDatabaseName = "db"
            )]
            IReadOnlyList<Document> changeList, TraceWriter log)
        {
            if (changeList != null && changeList.Count > 0)
            {
                log.Verbose("Documents modified " + changeList.Count);
                foreach (var change in changeList)
                {
                    log.Verbose("First document Id " + change.Id);
                }
            }

        }
    }