mapper.sd.forbid-nulls has the same behavior as
This mapper function returns the standard deviation of each sliding window. The location and elevation returned are those associated with the most recent value in the sliding window.
The standard deviation is the square root of the variance as computed by
mapper.sd.forbid-nulls function can only be applied to values of type LONG or DOUBLE, when applied to STRING or BOOLEAN it does not return any value.
If a value is NULL in the bucket, the result is NULL