Corrected PHP Error callsign value

application/views/qso/index.php

@@ -74,7 +74,7 @@
               <div class="form-row">
                 <div class="form-group col-md-9">
                   <label for="callsign"><?php echo lang('gen_hamradio_callsign'); ?></label><?php if ($this->optionslib->get_option('dxcache_url') != '') { ?>&nbsp;<i id="check_cluster" data-toggle="tooltip" data-original-title="Search DXCluster for latest Spot" class="fas fa-search"></i> <?php } ?>
-                  <input type="text" class="form-control" id="callsign" name="callsign" value="<?php echo $_GET['callsign']; ?>" required>
+                  <input type="text" class="form-control" id="callsign" name="callsign" value="<?php echo !empty($_GET['callsign']) ? $_GET['callsign'] : ''; ?>" required>
                   <small id="callsign_info" class="badge badge-secondary"></small> <a id="lotw_link"><small id="lotw_info" class="badge badge-success"></small></a>
                 </div>
                 <div class="form-group col-md-3 align-self-center">