That (and there was a similar suggestion above as well) doesn't help his problem.

  my $foo = ' ';  # or   my $foo = '';
  $foo = getFoo();
  if ( $foo eq "true" ){ ... }    # this will warn if $foo is undef
  $foo = $dbh->selectrow_array("select x from blah limit 1");
  if ( $foo eq "true" ){ ... }    # this will warn if $foo is undef
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In these cases, the original default value doesn't matter because it's overwritten later by a 'third party' (some sub or dbh call), and the hint to the Maintainer doesn't help cause it's something else (e.g. some db value) that's being stored.