Minor - format code, fix php error

public/main/admin/index.php

@@ -280,7 +280,7 @@ if (api_is_platform_admin()) {
         ];
         $items[] = [
             'url' => 'skill.php',
-            'label' => get_lang('Manage skillsLevels'),
+            'label' => get_lang('Manage skills levels'),
         ];
 
         $items[] = [

public/main/auth/my_progress.php

@@ -97,9 +97,9 @@ if (!empty($dates)) {
     $content .= '</div></div>';
 }
 
-if (true === api_get_configuration_value('private_messages_about_user_visible_to_user')) {
+if (api_get_configuration_value('private_messages_about_user_visible_to_user')) {
     $allowMessages = api_get_configuration_value('private_messages_about_user');
-    if (true === $allowMessages) {
+    if ($allowMessages) {
         // Messages
         $content .= Display::page_subheader2(get_lang('Messages'));
         $content .= MessageManager::getMessagesAboutUserToString(api_get_user_info());

public/main/inc/lib/message.lib.php

@@ -14,7 +14,7 @@ use Symfony\Component\HttpFoundation\File\UploadedFile;
 
 class MessageManager
 {
-    public static function getMessagesAboutUserToString(User $user, string $url): string
+    public static function getMessagesAboutUserToString(User $user, string $url = ''): string
     {
         $messages = Container::getMessageRepository()->getMessageByUser($user, Message::MESSAGE_TYPE_CONVERSATION);
         $html = '';
@@ -35,10 +35,15 @@ class MessageManager
                 );
                 $sender = $message->getSender();
 
+                $deleteButton = '';
+                if (!empty($url)) {
+                    $deleteButton = Display::url(get_lang('Delete'), $url.'&action=delete_message&message_id='.$messageId, ['class' => 'btn btn-danger']);
+                }
+
                 $content = $message->getContent().'<br />'.$date.'<br />'.
                     get_lang('Author').': '.$sender->getUsername().
                     '<br />'.
-                    Display::url(get_lang('Delete'), $url.'&action=delete_message&message_id='.$messageId, ['class' => 'btn btn-danger']);
+                    $deleteButton
                 ;
 
                 $html .= Display::panelCollapse(