Very sorry! After further testing, the actual problem I was having was that SUM returns a double, and I was putting it into an INT container without an explicit cast.
So, maybe this bug is a request to change the wiki to make this clear.
Also...let's actually say the opposite. We really should have AVG or some version of it return NULL if any NULL values are found. This is the default behavior in R, and for good reason...I will link to the description of why once I find it.
Basically, the argument is that when a sum, average, or variance depends on n in some sense, comparisons among these groups cannot be trusted. For example, if there are 5 nulls in a set of 20 variables, SUM / COUNT returns a different value than AVG...that is very unintuitive.