The message part of your regex isn't optional. Append a ? to make it so. Your use of the /g modifier there was misplaced - since you're already anchoring at the front and end of the string, the pattern can't match multiple times in the first place. Relying on the $_ variable can also make your code much shorter.

while(<IN>) {
     next if /^(\s*)("[^"]+")?$/;
     chomp;
}
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Update: [^*"] -> [^"]. Thanks sauoq.

Makeshifts last the longest.