If you know you are going to be trying to treat null strings as numbers, turn it off:
Then perlcritic will complain:
Warnings disabled at line 10, column 5. See page 431 of PBP. (Severity: 4)
Solution 1 (ugly): no warnings 'numeric'; ## no critic (TestingAndDebugging::ProhibitNoWarnings)
Solucion 2 (dangerous): add the following to ~/.perlcriticrc:
allow = numeric
(Please treat my english text just like Perl code, i.e. feel free to notify me of any syntax, grammar, style and/or spelling error. Thank you!).