How to fix An unhandled exception of type 'System.NullReferenceException' occurred in Microsoft.Threading.Tasks.dll ?

System.NullReferenceException was unhandled
Message: An unhandled exception of type 'System.NullReferenceException' occurred in Microsoft.Threading.Tasks.dll
Additional information: Object reference not set to an instance of an object.

public void SendEmail()
        {

            string emailTo = string.Empty; string emailFrom = string.Empty;
            string subject = string.Empty; string text = string.Empty;
            string html = string.Empty; string userName = string.Empty;
            string password = string.Empty;

            // Create the email object first, then add the properties.
            SendGridMessage myMessage = new SendGridMessage();
            myMessage.AddTo("test@gmail.com ");
            myMessage.From = new MailAddress("test@gmail.com", "User I am");
            myMessage.Subject = "Testing the SendGrid Library";
            myMessage.Text = "Hello World!";
            myMessage.Html = "";

            // Create credentials, specifying your user name and password.
            var credentials = new NetworkCredential("myUserName", "myPassword");

            // Create an Web transport for sending email, using credentials...
            var transportWeb = new Web(credentials);

            // Send the email.
            transportWeb.DeliverAsync(myMessage);
        }