Reduces a list to a single value by evaluating a formula for each item in the list, accumulating to a result value which is then passed to the next evaluation.
The iteration is done from the first item to the last item. The iteration starts by using the 1st item in the list as an initial accumulator value. Alternatively you can use REDUCE\_INIT function instead and provide an initial value.
If the list has only one item, that item is returned. If the list is empty, returns null.