Async System.Threading.Timer sometimes throwing null exception [closed]

Answer 1

I don't know why you get the NullReferenceException in your code, but I suggest to scrap the Timer approach altogether and replace it with a simpler Task.Delay in a loop:

var apiCallCts = new CancellationTokenSource();
var apiCallTask = Task.Run(async () =>
{
    while (true)
    {
        var delayTask = Task.Delay(TimeSpan.FromSeconds(10), apiCallCts.Token);
        await SomeApiCallAsync();
        await delayTask;
    }
});

And at the app shutdown:

apiCallCts.Cancel();

The above solution has a different behavior in case of an API failure. Instead of crashing the app, will silently stop calling the API. This is something that you'll have to consider.