GitLab

Use "if (!defined($thing)){}" instead of "if (!$thing){}" when $thing is

a string that can be 0 (zero).

Similarly use "if (exists( some hash compartment ))" for the same reason.

A couple of changes from "@{ function_returning_array_ref() }($index)"
to "function_returning_array_ref()->[$index]";

General cleanup in comments and code.

Passes the unit tests.