...
eval { $DT = DateTime->new( year => $year, time_zone => $tz ); };
return if $@;
...

##</code><code>##

The 'name' parameter (undef) to DateTime::TimeZone::new was an 'undef', which is not one of the allowed types: scalar
 at /idcom/weblive/extperl/lib/perl5/site_perl/5.8.5/DateTime/TimeZone.pm line 34
        DateTime::TimeZone::new('undef', 'name', 'undef') called at
/idcom/weblive/extperl/lib64/perl5/site_perl/5.8.5/x86_64-linux-thread-multi/DateTime.pm line 192
        DateTime::new('undef', 'year', 2010, 'time_zone', 'Europe/London') called at TZInfo.pm line 33
        TZInfo::get_dst_changes(2010, 'Europe/London') called at ./nz.pl line 1039

##</code><code>##

...
sub new
{
    my $class = shift;
    my %p = validate( @_, $NewValidate );
...

##</code><code>##

@_ set to:
$VAR1 = [
          'year',
          2010,
          'time_zone',
          'Europe/London'
        ];
%p set to:
$VAR1 = {};