diff --git a/admin/configuration.php b/admin/configuration.php
index 43d0b48da..ece27649e 100644
--- a/admin/configuration.php
+++ b/admin/configuration.php
@@ -350,7 +350,7 @@ switch ($page['section'])
     {
       $out = array();
       $order_by = trim($conf['order_by_inside_category']);
-      $order_by = str_replace('ORDER BY ', null, $order_by);
+      $order_by = str_replace('ORDER BY ', false, $order_by);
       $order_by = explode(', ', $order_by);
     }
 
diff --git a/include/template.class.php b/include/template.class.php
index cc1747bd6..b88d1a7dd 100644
--- a/include/template.class.php
+++ b/include/template.class.php
@@ -702,7 +702,7 @@ class Template
    */
   function block_html_head($params, $content)
   {
-    $content = trim($content);
+    $content = isset($content) ? trim($content) : '';
     if ( !empty($content) )
     { // second call
       $this->html_head_elements[] = $content;
@@ -718,7 +718,7 @@ class Template
    */
   function block_html_style($params, $content)
   {
-    $content = trim($content);
+    $content = isset($content) ? trim($content) : '';
     if ( !empty($content) )
     { // second call
       $this->html_style .= "\n".$content;
@@ -908,7 +908,7 @@ var s,after = document.getElementsByTagName(\'script\')[document.getElementsByTa
    */
   function block_footer_script($params, $content)
   {
-    $content = trim($content);
+    $content = isset($content) ? trim($content) : '';
     if ( !empty($content) )
     { // second call