Improve unit test (#1901)

lemonldap-ng-handler/t/65-Lemonldap-NG-Handler-PSGI-ServiceToken.t

@@ -26,6 +26,8 @@ init(
         exportedHeaders => {
             'test2.example.com' => {
                 'Auth-User' => '$uid',
+                'empty'     => undef,
+                'zero'      => "'0'",
             },
         }
     }
@@ -114,6 +116,13 @@ ok(
 ok( $res->[0] == 200, 'Code is 200' ) or explain( $res->[0], 200 );
 count(2);
 
+my %headers = @{ $res->[1] };
+ok( $headers{'zero'} eq '0', 'Found "zero" header with "0"' )
+  or print STDERR Data::Dumper::Dumper( $res->[1] );
+ok( $headers{'empty'} eq '', 'Found "empty" header without value' )
+  or print STDERR Data::Dumper::Dumper( $res->[1] );
+count(2);
+
 @headers = grep { /service|^XFromVH$/ } @{ $res->[1] };
 @values  = grep { /\.example\.com|^$sessionId$/ } @{ $res->[1] };
 ok( @headers == 2, 'Found 2 service headers' )