Display a message when BBM was not executed due to the table being empty

Overview

Sometimes, BBM cannot be sampled because the target table is empty. In such situations, we do not display anything for the reviewer.

Example: gitlab-org/gitlab!160740 (comment 2020198528)

Desired Outcome

  • Display a message informing that the BBM was not executed because the target table is empty
    • Important note: We need to account for empty tables for a different database that the BBM was targeted to. E.G: An migration targeting a table in the main database, that can be empty on ci.