if (activityName != null && string.IsNullOrWhiteSpace(activityName))
{
throw new ArgumentException(nameof(activityName) + " is empty or white spaces.", nameof(activityName));
}
However, string.IsNullOrWhiteSpace(activityName) can be true regardless of activityName being null or not.
The intention of the test is to catch only the non-null empty or white space values.
I am a bit confused because you are mentioning S4457: Parameter validation in "async"/"await" methods should be wrapped and later on you are talking about whether activityName can be null which isn’t checked by this rule.
Could you let me know which problem you are facing?