'use' implies a BEGIN block. Also, the DEBUG && BEGIN {} looks suspect to me. What you want instead is likely:

use constant DEBUG => 1;
BEGIN {
  if (! DEBUG) {
    require CGI::Carp;
    import  CGI::Carp qw/ fatalsToBrowser /;
  }
}
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--jwest

-><- -><- -><- -><- -><-
All things are Perfect
    To every last Flaw
    And bound in accord
         With Eris's Law
 - HBT; The Book of Advice, 1:7