In statistical MCL functions, null values will not be counted. For example, when we apply the Ave FP model (see MCL Tutorial) to the the horse Cyber Gulch in the 633 rd race of season 1999-2000, we will get the .NULL. result. It is because at the time of the race, the horse Cyber Gulch has only started once. In that start, its finishing position was 13. Thus, the function HrFP(1) returns 13 (column FP(1)) and function HrFP(2) returns .NULL.
When a statistical MCL function finds no data to process, the function will return a null value as well.