diff --git a/templates/clean-blog/config.inc.php b/templates/clean-blog/config.inc.php
index 691bc820..647dbb14 100644
--- a/templates/clean-blog/config.inc.php
+++ b/templates/clean-blog/config.inc.php
@@ -215,7 +215,7 @@ $template_config = array(
 
 // Collapse template options into groups.
 $template_global_config = array('navigation' => true);
-$template_loaded_config = serendipity_loadThemeOptions($template_config, $serendipity['smarty_vars']['template_option'], true);
+$template_loaded_config = serendipity_loadThemeOptions($template_config, $serendipity['smarty_vars']['template_option'] ?? null, true);
 serendipity_loadGlobalThemeOptions($template_config, $template_loaded_config, $template_global_config);
 
 $navlinks_collapse = array( 'use_corenav', 'amount');
diff --git a/templates/clean-blog/content.tpl b/templates/clean-blog/content.tpl
index 46947f26..e48fea82 100644
--- a/templates/clean-blog/content.tpl
+++ b/templates/clean-blog/content.tpl
@@ -4,9 +4,9 @@
       <div class="alert alert-danger"><h4>{$CONST.SEARCH}</h4><span class="fa-stack" aria-hidden="true"><i class="fa fa-circle-thin fa-stack-2x"></i><i class="fa fa-exclamation fa-stack-1x"></i></span> {$content_message}</div>
 {elseif $searchresult_results}
       <div class="alert alert-success"><h4>{$CONST.SEARCH}</h4><span class="fa-stack" aria-hidden="true"><i class="fa fa-circle-thin fa-stack-2x"></i><i class="fa fa-check fa-stack-1x"></i></span> {$content_message}</div>
-{elseif $subscribe_confirm_error}
+{elseif isset($subscribe_confirm_error) && $subscribe_confirm_error}
       <div class="alert alert-danger"><h4>{$CONST.ERROR}</h4><span class="fa-stack" aria-hidden="true"><i class="fa fa-circle-thin fa-stack-2x"></i><i class="fa fa-exclamation fa-stack-1x"></i></span> {$content_message}</div>
-{elseif $subscribe_confirm_success}
+{elseif isset($subscribe_confirm_success) && $subscribe_confirm_success}
       <div class="alert alert-success"><h4>{$CONST.SUCCESS}</h4><span class="fa-stack" aria-hidden="true"><i class="fa fa-circle-thin fa-stack-2x"></i><i class="fa fa-check fa-stack-1x"></i></span> {$content_message}</div>
 {elseif $content_message}
    <div class="alert alert-info"><span class="fa-stack" aria-hidden="true"><i class="fa fa-circle-thin fa-stack-2x"></i><i class="fa fa-info fa-stack-1x"></i></span>  {$content_message}</div>
diff --git a/templates/clean-blog/entries.tpl b/templates/clean-blog/entries.tpl
index 99f36689..c67f8182 100644
--- a/templates/clean-blog/entries.tpl
+++ b/templates/clean-blog/entries.tpl
@@ -5,7 +5,7 @@
     <article id="post_{$entry.id}" class="post{if !$is_single_entry and not $entry.is_extended and not $is_preview}-preview{/if} serendipity_entry{if $dategroup.is_sticky} sticky{/if}" role="article">
     {if !$is_single_entry and not $entry.is_extended and not $is_preview}
         <a href="{$entry.link}"><h2 class="post-title">{$entry.title}</h2>
-        {if $entry.properties.entry_subtitle}
+        {if isset($entry.properties.entry_subtitle) and $entry.properties.entry_subtitle}
             <h3 class="post-subtitle">{$entry.properties.entry_subtitle|escape}</h3>
         {elseif $template_option.subtitle_use_entrybody==true && $template_option.entrybody_detailed_only == true}
             <h3 class="post-subtitle">{$entry.body|@strip_tags|@strip|@truncate:70:" ..."}</h3>
diff --git a/templates/clean-blog/index.tpl b/templates/clean-blog/index.tpl
index a62eaaa7..10b3a7a6 100644
--- a/templates/clean-blog/index.tpl
+++ b/templates/clean-blog/index.tpl
@@ -8,7 +8,7 @@
     <meta name="generator" content="Serendipity v.{$serendipityVersion}">
     <title>{$head_title|default:$blogTitle}{if $head_subtitle} | {$head_subtitle}{/if}</title>
 {* CANONICAL *}
-    {if ($view == "entry" || $view == "start" || $view == "feed" || $view == "plugin" || $staticpage_pagetitle != "" || $robots_index == 'index')}
+    {if ($view == "entry" || $view == "start" || $view == "feed" || $view == "plugin" || (isset($staticpage_pagetitle) && $staticpage_pagetitle != "") || $robots_index == 'index')}
        <meta name="robots" content="index,follow">
     {else}
        <meta name="robots" content="noindex,follow">
@@ -48,13 +48,13 @@
         {else}
             <style type="text/css">.intro-header {ldelim}background-image: url('{if $template_option.entry_default_header_image}{$template_option.entry_default_header_image}{else}{serendipity_getFile file="img/post-bg.jpg"}{/if}');{rdelim}</style> 
         {/if}
-    {elseif $staticpage_pagetitle && !$plugin_contactform_name}
+    {elseif (isset($staticpage_pagetitle) && $staticpage_pagetitle) && ! (isset($plugin_contactform_name) && $plugin_contactform_name)}
         {if $staticpage_custom.staticpage_header_image}
             <style type="text/css">.intro-header {ldelim}background-image: url('{$staticpage_custom.staticpage_header_image}');{rdelim}</style>           
         {else}
             <style type="text/css">.intro-header {ldelim}background-image: url('{if $template_option.staticpage_header_image}{$template_option.staticpage_header_image}{else}{serendipity_getFile file="img/about-bg.jpg"}{/if}');{rdelim}</style>
         {/if}
-    {elseif $plugin_contactform_name}
+    {elseif (isset($plugin_contactform_name) && $plugin_contactform_name)}
         <style type="text/css">.intro-header {ldelim}background-image: url('{if $template_option.contactform_header_image}{$template_option.contactform_header_image}{else}{serendipity_getFile file="img/contact-bg.jpg"}{/if}');{rdelim}</style>
     {elseif $view=="archive"}
         <style type="text/css">.intro-header {ldelim}background-image: url('{if $template_option.archive_header_image}{$template_option.archive_header_image}{else}{serendipity_getFile file="img/archive-bg.jpg"}{/if}');{rdelim}</style>