Function filter_null_mask

fn filter_null_mask(
    nulls: Option<&NullBuffer>,
    predicate: &FilterPredicate,
) -> Option<(usize, Buffer)>

Computes a new null mask for data based on predicate

If the predicate selected no null-rows, returns None, otherwise returns Some((null_count, null_buffer)) where null_count is the number of nulls in the filtered output, and null_buffer is the filtered null buffer