diff --git a/application/models/Logbook_model.php b/application/models/Logbook_model.php
index 758a04951..5c5af85b3 100644
--- a/application/models/Logbook_model.php
+++ b/application/models/Logbook_model.php
@@ -21,7 +21,7 @@ class Logbook_model extends CI_Model {
     $callsign = str_replace('Ø', '0', $this->input->post('callsign'));
     // Join date+time
     $datetime = date("Y-m-d",strtotime($this->input->post('start_date')))." ". $this->input->post('start_time');
-    if ($this->input->post('end_time') != null) {
+    if ( ($this->input->post('end_time') ?? '') != '') {
         $datetime_off = date("Y-m-d",strtotime($this->input->post('start_date')))." ". $this->input->post('end_time');
         // if time off < time on, and time off is on 00:xx >> add 1 day (concidering start and end are between 23:00 and 00:59) //
         $_tmp_datetime_off = strtotime($datetime_off);