Merge branch '126-bug-nil-division-when-estimated_number_of_batches-is-not-set' into 'master'

Add a fix for cases were total_tuple_count is nil

Closes #126

See merge request !157



Merged-by: Diogo Frazão <dfrazao@gitlab.com>
Approved-by: Diogo Frazão <dfrazao@gitlab.com>
Co-authored-by: Leonardo Rosa <ldarosa@gitlab.com>