Check for empty string and substitute a number instead: 
$inc ||= 0;
$exp ||= 0;

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Those expressions transform to $var = $var || 0; and $var is false when it's zero-ish, undef or an empty string. When it's zero, we're not changing anything; we should not get undef in this program; and the empty string the cause of this warning, which we're replacing with 0.

In reply to Re: use warnings is complaining by Anonymous Monk
in thread use warnings is complaining by Anonymous Monk

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