Spending a lot of time developing websites with Sitecore means I've reported my fair share of bugs to support. One particular issue that I came across in 6.6 a while back stands out as my "favourite" issue I've reported – just because the error stops a lot of developers in their tracks thinking "how on earth can this happen?". If you wrote this code, would you think it could crash?
Well it can crash. And to a less experienced developer it can be a very confusing error: