average method
Returns the average of all the values in this iterable.
Example:
[2, 2, 4, 8].average(); // 4.
[2, 2, 4, 8].average((i) => i + 1); // 5.
[].average() // null.
Implementation
num? average([num Function(E)? value]) {
if (isEmpty) return null;
return sum(value) / length;
}