Exception 'Error' with message 'Object of class app1\modules\v1\resources\cms\CmsSeoResource could not be converted to string' 

in /disk_1/www/cz/agneweb/api/app1/modules/v1/models/cms/SitemapModel.php:91

Stack trace:
#0 /disk_1/www/cz/agneweb/api/app1/modules/v1/controllers/cms/SitemapController.php(43): app1\modules\v1\models\cms\SitemapModel->generateSitemap()
#1 [internal function]: app1\modules\v1\controllers\cms\SitemapController->actionGenerate(NULL, 'pages_cs-CZ')
#2 /disk_1/www/cz/agneweb/api/vendor/yiisoft/yii2/base/InlineAction.php(57): call_user_func_array(Array, Array)
#3 /disk_1/www/cz/agneweb/api/vendor/yiisoft/yii2/base/Controller.php(181): yii\base\InlineAction->runWithParams(Array)
#4 /disk_1/www/cz/agneweb/api/vendor/yiisoft/yii2/base/Module.php(534): yii\base\Controller->runAction('generate', Array)
#5 /disk_1/www/cz/agneweb/api/vendor/yiisoft/yii2/web/Application.php(104): yii\base\Module->runAction('v1/cms/sitemap/...', Array)
#6 /disk_1/www/cz/agneweb/api/vendor/yiisoft/yii2/base/Application.php(392): yii\web\Application->handleRequest(Object(yii\web\Request))
#7 /disk_1/www/cz/agneweb/api/app1/web/index.php(17): yii\base\Application->run()
#8 {main}