FIX: fix history handling - null values were not updated

app/Handlers/History.php

@@ -39,8 +39,8 @@ class History implements HistoryHandler
                 break;
             default:
                 return trans('admin/history.changedFromTo', [
-                    'from' => $changeset->old_value,
-                    'to'   => $changeset->new_value
+                    'from' => is_null($changeset->old_value) ? trans('admin/history.emptyValue') : $changeset->old_value,
+                    'to'   => is_null($changeset->new_value) ? trans('admin/history.emptyValue') : $changeset->new_value,
                 ]);
                 break;
         }

app/Models/Content.php

@@ -125,14 +125,15 @@ class Content extends Model
 
         foreach ($fields as $fieldDB => $fieldRequest) {
             // ignore non-existing fields
-            if (!isset($this->$fieldDB) || !isset($request[$fieldRequest])) {
+            if ((!isset($this->$fieldDB) && !is_null($this->$fieldDB)) || (!isset($request[$fieldRequest]) && !is_null($request[$fieldRequest]))) {
                 continue;
             }
 
             // remove any whitespaces around real content
+            if (!is_null($request[$fieldRequest]))
             $request[$fieldRequest] = trim($request[$fieldRequest]);
 
-            if ($this->$fieldDB != $request[$fieldRequest]) {
+            if (trim($this->$fieldDB) != $request[$fieldRequest]) {
 
                 // setup history object
                 $history = [

resources/lang/en/admin/history.php

@@ -9,6 +9,7 @@ return [
     'columnStatus'          => 'Page visibility',
     'columnTemplate'        => 'Template',
     'columnIs_homepage'     => 'Homepage',
+    'emptyValue'            => '<em>none</em>',
     'changedFromTo'         => 'Changed from <del>:from</del> to <ins>:to</ins>',
     'numOfChanges'          => 'One change|:count changes',
     'diff'                  => 'Difference',