$ cat 666463.pl
use strict;
use warnings;

use Log::Log4perl;
use Log::Dispatch::FileRotate;

my $conf = q(
  log4perl.category.foo = DEBUG, FileRotateAppender

  log4perl.appender.FileRotateAppender           = Log::Dispatch::FileRotate
  log4perl.appender.FileRotateAppender.filename  = foo.log
  log4perl.appender.FileRotateAppender.mode      = append
  log4perl.appender.FileRotateAppender.size      = 100000
  log4perl.appender.FileRotateAppender.max       = 5
  log4perl.appender.FileRotateAppender.layout    = PatternLayout
  log4perl.appender.FileRotateAppender.layout.ConversionPattern=[%p] %d %M %F:%L:- %m%n
);
Log::Log4perl::init( \$conf );
my $log = Log::Log4perl::get_logger("foo");

sub check_something {
  my $something = shift;
  $log->debug(qq{something:'$something'}) if $log->is_debug();
  if (!defined($something)) {
    $log->error(qq{something is nothing!}) if $log->is_error();
  }
  return $something;
}

# ------ main ------
check_something(q{hello});
check_something();

__END__

##</code><code>##

$ perl 666463.pl
Use of uninitialized value in concatenation (.) or string at 666463.pl line 23.

##</code><code>##

$ tail foo.log
[DEBUG] 2008/02/06 10:45:00 main::check_something 666463.pl:23:- something:'hello'
[DEBUG] 2008/02/06 10:45:00 main::check_something 666463.pl:23:- something:''
[ERROR] 2008/02/06 10:45:00 main::check_something 666463.pl:24:- something is nothing!