@hf_value_exists not working as expected

kamailio/registrar-role.cfg

@@ -254,14 +254,10 @@ route[SAVE_LOCATION]
         }
     }
 
-    if(@hf_value_exists.contact.expires == "1") {
-        $var(expires) = @contact.expires;
+    if($expires(max) != $null) {
+        $var(expires) = $expires(max);
     } else {
-        if(is_present_hf("Expires")) {
-           $var(expires) = $hdr(Expires);
-        } else {
-           $var(expires) = REGISTRAR_MIN_EXPIRES;
-        }
+        $var(expires) = REGISTRAR_MIN_EXPIRES;
     }
 
     if($var(expires) == 0) {