Possible NullReference Exception

[tmacharia]

https://github.com/AfricasTalkingLtd/africastalking.Net/blob/640b1955ffbe7f28da0a14fd1adfdab08813bad7/AfricasTalkingCS/AfricasTalkingGateway.cs#L398

Hi, this check will fail when a string in null since you can't call .Length on a null string object.

I would suggest using String.IsNullOrWhiteSpace(String) to do the check.

You can create a test case wherein you pass null for phoneNumber/shortCode/keyWord and see that a NullObjectReferenceException is thrown instead of the anticipated AfricasTalkingGatewayException

[TheBeachMaster]

Nice catch, would you mind sending a PR with a minor version bump...

[tmacharia]

Let me see.