MT#62763 Use «return» instead of «return undef»

Warned-by: perlcritic
Fixes: Subroutines::ProhibitExplicitReturnUndef
Change-Id: If26f11feb4c784126ad8e0adb9575e30e8d3aaa3

sandbox/billing_mapping_effective_date.t

@@ -639,7 +639,7 @@ sub get_actual_billing_mapping_old {
                     '+as' => [ 'billing_mapping_id' ],
                 })->first;
     return $contract->get_column("billing_mapping_id") if $contract;
-    return undef;
+    return;
 
 }
 

sandbox/generate_logfile_data_inventory.pl

@@ -622,7 +622,7 @@ sub _deserialize_messagesargs {
     my $args = eval $_line;
     if ($@) {
         warn($_line ."\n" .$@);
-        return undef;
+        return;
     } else {
         return $args;
     }