updated

Author: landofcoder

Block/Adminhtml/System/ListLicense.php

@@ -238,7 +238,7 @@ public function render(\Magento\Framework\Data\Form\Element\AbstractElement $ele
                 if(!$value && isset($_extension['key']) && $_extension['key']){
                     $value = $_extension['key'];
                 }
-                $value = trim($value);
+                $value = @trim($value);
                 $baseUrl = $this->_storeManager->getStore()->getBaseUrl(
                     \Magento\Framework\UrlInterface::URL_TYPE_WEB
                     );

view/frontend/templates/html/head.phtml

@@ -2,8 +2,8 @@
 $data = $this->helper("Lof\All\Helper\Data");
 $customCss = $data->getConfig('custom_css');
 if ($customCss) {
-    $customCss = strip_tags($customCss);
-    $customCss = trim($customCss);
+    $customCss = @strip_tags($customCss);
+    $customCss = @trim($customCss);
 }
 ?>
 <?php if ($customCss) : ?>