diff --git a/src/warden-client/bin/sender.pl b/src/warden-client/bin/sender.pl
index 183d994f6fa300b179d01a62cc7eefe0c427b10e..d950d63383916405294c0b2e18ca559d50a51219 100755
--- a/src/warden-client/bin/sender.pl
+++ b/src/warden-client/bin/sender.pl
@@ -35,7 +35,7 @@ switch (int(rand(9) + 0.5)) {
   case 8 { $type = 'webattack'; }
   case 9 { $type = 'other'; }
   }
-  
+
 my $source_type = "";
 switch (int(rand(2) + 0.5)) {
   case 0 { $source_type = 'IP'; }
@@ -58,7 +58,7 @@ switch (int(rand(5) + 0.5)) {
   case 2 { $target_port = '25'; }
   case 3 { $target_port = '443'; }
   case 4 { $target_port = '3389'; }
-  case 5 { $target_port = 'null'; }
+  case 5 { $target_port = undef; }
   }
 
 my $attack_scale = (int(rand(100000) + 0.5) + 1000);
@@ -68,13 +68,13 @@ my $note = "tohle je takova normalni jednoducha poznamka";
 my $priority = "";
 switch (int(rand(1) + 0.5)) {
   case 0 { $priority = int(rand(255) + 0.5); }
-  case 1 { $priority = 'null'; }
+  case 1 { $priority = undef; }
   }
   
 my $timeout = "";
 switch (int(rand(1) + 0.5)) {
   case 0 { $timeout = int(rand(255) + 0.5); }
-  case 1 { $timeout = 'null'; }
+  case 1 { $timeout = undef; }
   } 
 
 my @event = (
diff --git a/src/warden-client/doc/example-sender.pl.txt b/src/warden-client/doc/example-sender.pl.txt
index 24c6dd114c0441bfb6bff331bb8aa1ef9449b5c2..79bae989ff793ae392a4bfa2d03456d8f54c00d5 100644
--- a/src/warden-client/doc/example-sender.pl.txt
+++ b/src/warden-client/doc/example-sender.pl.txt
@@ -32,7 +32,7 @@ my $target_proto 	= "TCP";
 my $target_port 	= "22";
 my $attack_scale 	= "1234567890";
 my $note 		= "important note or comment";
-my $priority 		= "null";
+my $priority 		= undef;
 my $timeout 		= "20";
 
 my @event 		= ($service, $detected, $type, $source_type, $source,