|You're making the assumption that the method that is throwing the null reference is inside your task. What's interesting is that you have failed to apply any forms of input guards to SearchMostLessViewsAsync and you're assuming you actually have values coming in. It wouldn't surprise me if the null reference you are seeing occurred in this call:
new Dictionary<string, string>()
If any of those is null, you'll get a null reference because you're calling
ToString() on it. The bottom line is that you shouldn't make assumptions about where exceptions are occurring; look at the whole part of the code.