Merge pull request #2404 from Jasrags/master

apps/advanced/frontend/widgets/Alert.php

@@ -48,6 +48,7 @@ class Alert extends \yii\bootstrap\Widget
 		$appendCss = isset($this->options['class']) ? ' ' . $this->options['class'] : '';
 
 		foreach ($flashes as $type => $message) {
+			if (isset($this->alertTypes[$type])) {
 				/* initialize css class for each alert box */
 				$this->options['class'] = $this->alertTypes[$type] . $appendCss;
 
@@ -63,4 +64,5 @@ class Alert extends \yii\bootstrap\Widget
 				$session->removeFlash($type);
 			}
 		}
+	}
 }