mapper.sum.forbid-nulls has the same behavior as
This mapper function computes the sum of all the values found in the sliding window. The associated location and elevation are those of the most recent tick of the window.
mapper.sum.forbid-nulls function can only be applied to values of type LONG or DOUBLE, it will produce no value for types STRING and BOOLEAN.
If a value is NULL in the bucket, the result is NULL.