diff --git a/templates/timeline/comments.tpl b/templates/timeline/comments.tpl
index 502b0f37..af3ecfa2 100644
--- a/templates/timeline/comments.tpl
+++ b/templates/timeline/comments.tpl
@@ -14,7 +14,7 @@
     <li id="comment-{$comment.id}" class="comment-list-item">
         <a id="c{$comment.id}"></a>
         <div id="div-comment-{$comment.id}" class="comment_any{cycle values=" comment_odd, comment_even"} comment_author_{$comment.author|@makeFilename} {if ($entry.author == $comment.author) && ($entry.email == $commentform_entry.email)}comment_author_self{/if}">
-            {if $comment.avatar}
+            {if isset($comment.avatar) and $comment.avatar}
                     {$comment.avatar}
             {/if}                
             <div class="comment-list-item-body">
@@ -42,7 +42,7 @@
                     {/if}                        
                     
                     {if $entry.allow_comments AND $comment.body != 'COMMENT_DELETED'}
-                        <a class="comment-reply-link btn btn-sm btn-default btn-theme" href="#serendipity_CommentForm" id="serendipity_reply_{$comment.id}" onclick="document.getElementById('serendipity_replyTo').value='{$comment.id}'; {$comment_onchange}" title="{$CONST.REPLY}"><i class="fas fa-lg fa-reply"></i><span class="sr-only"> {$CONST.REPLY}</span></a>
+                        <a class="comment-reply-link btn btn-sm btn-default btn-theme" href="#serendipity_CommentForm" id="serendipity_reply_{$comment.id}" onclick="document.getElementById('serendipity_replyTo').value='{$comment.id}'; {if isset($comment_onchange)}{$comment_onchange}{/if}" title="{$CONST.REPLY}"><i class="fas fa-lg fa-reply"></i><span class="sr-only"> {$CONST.REPLY}</span></a>
                         <div id="serendipity_replyform_{$comment.id}"></div>
                     {/if}
                 </div>
diff --git a/templates/timeline/config.inc.php b/templates/timeline/config.inc.php
index 06a2c7c0..a489cc37 100644
--- a/templates/timeline/config.inc.php
+++ b/templates/timeline/config.inc.php
@@ -9,23 +9,27 @@ $serendipity['smarty']->assign(array('currpage'  => "http://".$_SERVER['HTTP_HOS
 
 $serendipity['smarty']->assign('archiveURL', serendipity_rewriteURL(PATH_ARCHIVE));
 
-if ($serendipity['GET']['adminModule'] == 'templates' || $serendipity['POST']['adminModule'] == 'templates' || $serendipity['GET']['adminAction'] == 'cattemplate') {
-    $css_files = glob(dirname(__FILE__) . '/*_style.css');
-    foreach($css_files AS $css_file) {
-        $css_file = str_replace('_style.css', '', basename($css_file));
-        if (!isset($colorsets[$css_file])) {
-            $colorsets[$css_file] = $css_file;
+if (isset($serendipity['GET']['adminModule']) || isset($serendipity['POST']['adminModule'])) {
+    if ($serendipity['GET']['adminModule'] == 'templates' || $serendipity['POST']['adminModule'] == 'templates' || $serendipity['GET']['adminAction'] == 'cattemplate') {
+        $css_files = glob(dirname(__FILE__) . '/*_style.css');
+        foreach($css_files AS $css_file) {
+            $css_file = str_replace('_style.css', '', basename($css_file));
+            if (!isset($colorsets[$css_file])) {
+                $colorsets[$css_file] = $css_file;
+            }
         }
     }
 }
 
-if ($serendipity['GET']['adminModule'] == 'templates' || $serendipity['POST']['adminModule'] == 'templates' || $serendipity['GET']['adminAction'] == 'cattemplate') {
-    $skin_files = glob(dirname(__FILE__) . '/*_skin.css');
-    $skinsets[$skin_file] = 'light'; // light is default, but light_skin.css does not exist as light styles are written into style.css
-    foreach($skin_files AS $skin_file) {
-        $skin_file = str_replace('_skin.css', '', basename($skin_file));
-        if (!isset($skinsets[$skin_file])) {
-            $skinsets[$skin_file] = $skin_file;
+if (isset($serendipity['GET']['adminModule']) || isset($serendipity['POST']['adminModule'])) {
+    if ($serendipity['GET']['adminModule'] == 'templates' || $serendipity['POST']['adminModule'] == 'templates' || $serendipity['GET']['adminAction'] == 'cattemplate') {
+        $skin_files = glob(dirname(__FILE__) . '/*_skin.css');
+        $skinsets[$skin_file] = 'light'; // light is default, but light_skin.css does not exist as light styles are written into style.css
+        foreach($skin_files AS $skin_file) {
+            $skin_file = str_replace('_skin.css', '', basename($skin_file));
+            if (!isset($skinsets[$skin_file])) {
+                $skinsets[$skin_file] = $skin_file;
+            }
         }
     }
 }
@@ -122,14 +126,14 @@ $template_config = array(
         'name'          => THEME_COLORSET,
         'type'          => 'select',
         'default'       => 'green',
-        'select_values' => $colorsets
+        'select_values' => $colorsets ?? []
     ),   
     array(
         'var'           => 'skinset',
         'name'          => THEME_SKINSET,
         'type'          => 'select',
         'default'       => 'light',
-        'select_values' => $skinsets
+        'select_values' => $skinsets ?? []
     ),      
     array(
         'var'           => 'header_img',
@@ -229,7 +233,7 @@ $serendipity['smarty']->assign_by_ref('FooterSidebarElements', $FooterSidebarEle
 
 
 $template_global_config = array('navigation' => true);
-$serendipity['template_loaded_config'] = $template_loaded_config = serendipity_loadThemeOptions($template_config, $serendipity['smarty_vars']['template_option'], true);
+$serendipity['template_loaded_config'] = $template_loaded_config = serendipity_loadThemeOptions($template_config, $serendipity['smarty_vars']['template_option'] ?? '', true);
 serendipity_loadGlobalThemeOptions($template_config, $template_loaded_config, $template_global_config);
 
 
@@ -297,8 +301,8 @@ for ($i = 0; $i < $template_loaded_config['social_icons_amount']; $i++) {
         'default'       => '#',
     );
     $socialicons[] = array(
-        'service'           => $template_loaded_config['social_icon' . $i . 'service'],
-        'url'               => $template_loaded_config['social_icon' . $i . 'url'],
+        'service'           => $template_loaded_config['social_icon' . $i . 'service'] ?? '',
+        'url'               => $template_loaded_config['social_icon' . $i . 'url'] ?? '',
     );    
 }
 $serendipity['smarty']->assign_by_ref('socialicons', $socialicons);
diff --git a/templates/timeline/content.tpl b/templates/timeline/content.tpl
index 7e5699e9..e2c520f4 100644
--- a/templates/timeline/content.tpl
+++ b/templates/timeline/content.tpl
@@ -67,7 +67,7 @@
     </div>
 </div>
 
-{elseif $subscribe_confirm_error}
+{elseif isset($subscribe_confirm_error) and $subscribe_confirm_error}
 <div id="search-block" class="row">
     <div class="col-md-8 col-md-offset-2">       
         <div id="search-response" class="panel panel-danger">
@@ -82,7 +82,7 @@
     </div>
 </div>
 
-{elseif $subscribe_confirm_success}
+{elseif isset($subscribe_confirm_success) and $subscribe_confirm_success}
 <div id="search-block" class="row">
     <div class="col-md-8 col-md-offset-2">
         <div id="search-response" class="panel panel-success">
@@ -96,7 +96,7 @@
         </div>    
     </div>
 </div>
-{elseif $content_message}
+{elseif isset($content_message) and $content_message}
 <div id="search-block" class="row">
     <div class="col-md-8 col-md-offset-2">
         <div class="alert alert-info alert-dismissible fade in" role="alert">
diff --git a/templates/timeline/entries.tpl b/templates/timeline/entries.tpl
index 9b490bfa..676a6c86 100644
--- a/templates/timeline/entries.tpl
+++ b/templates/timeline/entries.tpl
@@ -1,6 +1,6 @@
 {serendipity_hookPlugin hook="entries_header" addData="$entry_id"}
 
-{if $template_option.display_as_timeline and $entries and !$is_single_entry and not $entry.is_extended and not $is_preview}{* THIS IS OUR FRONTPAGE SCENARIO - OPEN TIMELINE*}
+{if $template_option.display_as_timeline and $entries and !$is_single_entry and not isset($entry.is_extended) and not $is_preview}{* THIS IS OUR FRONTPAGE SCENARIO - OPEN TIMELINE*}
     <ul class="timeline">
     {assign var="prevmonth" value=''}
 {/if}
@@ -25,10 +25,10 @@
                     <div class="timeline-badge"><i class="far fa-dot-circle" aria-hidden="true"></i></div>
                     <div class="timeline-panel">
                         <div class="timeline-heading">
-                            {if $entry.properties.timeline_image|is_in_string:'<iframe,<embed,<object'}{* we assume this is a video, just emit the contents of the var *}
+                            {if isset($entry.properties.timeline_image) and $entry.properties.timeline_image|is_in_string:'<iframe,<embed,<object'}{* we assume this is a video, just emit the contents of the var *}
                                 {$entry.properties.timeline_image}
                             {else}
-                                <a href="{$entry.link}" title="{$entry.title}"><img class="img-responsive" {if $entry.properties.timeline_image}src="{$entry.properties.timeline_image}"{else}src="{serendipity_getFile file='img/image_unavailable.jpg'}"{/if} alt=""/></a>
+                                <a href="{$entry.link}" title="{$entry.title}"><img class="img-responsive" {if isset($entry.properties.timeline_image) and $entry.properties.timeline_image}src="{$entry.properties.timeline_image}"{else}src="{serendipity_getFile file='img/image_unavailable.jpg'}"{/if} alt=""/></a>
                             {/if}
                         </div>
                         <div class="timeline-body">
@@ -46,13 +46,13 @@
                     </li>
                     {assign var="prevmonth" value=$entry.timestamp|@formatTime:"%B"}
             {else}{* not using timeline - use blog format instead *}
-                {if $entry.body || $entry.properties.timeline_image}
+                {if $entry.body || isset($entry.properties.timeline_image) and $entry.properties.timeline_image}
                     <div class="row each-blogstyle-entry">
                         <div class="col-md-5 blogstyle-post-thumb">
-                            {if $entry.properties.timeline_image|is_in_string:'<iframe,<embed,<object'}{* we assume this is a video, just emit the contents of the var *}
+                            {if isset($entry.properties.timeline_image) and  $entry.properties.timeline_image|is_in_string:'<iframe,<embed,<object'}{* we assume this is a video, just emit the contents of the var *}
                                 <div>{$entry.properties.timeline_image}</div>
                             {else}
-                                <a href="{$entry.link}" title="{$entry.title}"><img class="img-responsive" {if $entry.properties.timeline_image}src="{$entry.properties.timeline_image}"{else}src="{serendipity_getFile file='img/image_unavailable.jpg'}"{/if} alt=""/></a>
+                                <a href="{$entry.link}" title="{$entry.title}"><img class="img-responsive" {if isset($entry.properties.timeline_image) and $entry.properties.timeline_image}src="{$entry.properties.timeline_image}"{else}src="{serendipity_getFile file='img/image_unavailable.jpg'}"{/if} alt=""/></a>
                             {/if}                        
                         </div>
                         <div class="col-md-7 blogstyle-post-body">
@@ -83,7 +83,7 @@
                 {if $is_preview}
                     {append var='entry' value=$smarty.session.save_entry_POST.properties index='properties'}{* gives us access to entry properties in preview *}
                 {/if}
-                {if $entry.properties.timeline_image}
+                {if isset($entry.properties.timeline_image) and $entry.properties.timeline_image}
                     {if $entry.properties.timeline_image|is_in_string:'<iframe,<embed,<object'}{* we assume this is a video, just emit the contents of the var *}
                         {$entry.properties.timeline_image}
                     {else}
@@ -277,7 +277,7 @@
 {/if}
 
 
-{if $footer_info or $footer_prev_page or $footer_next_page}
+{if not $is_single_entry and ($footer_info or $footer_prev_page or $footer_next_page)}
     <div class='serendipity_pageSummary'>
         {if $footer_info}
             <p class="summary serendipity_center">{$footer_info}</p>
diff --git a/templates/timeline/index.tpl b/templates/timeline/index.tpl
index a2c78086..0d6e5c76 100644
--- a/templates/timeline/index.tpl
+++ b/templates/timeline/index.tpl
@@ -7,7 +7,7 @@
     <meta http-equiv="X-UA-Compatible" content="IE=edge">
     <meta name="viewport" content="width=device-width, initial-scale=1">
     <meta name="generator" content="Serendipity v.{$serendipityVersion}">
-    {if ($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) and $staticpage_pagetitle != "") || (isset($robots_index) and $robots_index == 'index'))}
         <meta name="robots" content="index,follow">
     {else}
         <meta name="robots" content="noindex,follow">
@@ -112,7 +112,7 @@
                 {/if}
             </h2>
             
-            {if $footer_totalPages >1 && !isset($staticpage_pagetitle)}
+            {if isset($footer_totalPages) and $footer_totalPages > 1 && !isset($staticpage_pagetitle)}
                 <nav class="pagination pull-right">
                     {assign var="paginationStartPage" value="`$footer_currentPage-3`"}
                     {if $footer_currentPage+3 > $footer_totalPages}
@@ -154,7 +154,7 @@
 {* MAIN CONTENT *}
     <div class="container content">
         <div class="row">
-            <main class="{if ($rightSidebarElements > 0 && $staticpage_pagetitle =='') || ($rightSidebarElements > 0 && $staticpage_pagetitle !='' && $staticpage_custom.show_sidebars != 'false')}col-md-9{else}col-md-12{/if} mainpanel">
+            <main class="{if isset($rightSidebarElements) and ($rightSidebarElements > 0 && (!isset($staticpage_pagetitle) or $staticpage_pagetitle =='')) || isset($rightSidebarElements) and ($rightSidebarElements > 0 && (isset($staticpage_pagetitle) and $staticpage_pagetitle != '') && $staticpage_custom.show_sidebars != 'false')}col-md-9{else}col-md-12{/if} mainpanel">
                 {if $view=='404'}
                     <div id="search-block" class="row">
                         <div class="col-md-8 col-md-offset-2">
@@ -205,7 +205,7 @@
                     {$CONTENT}
                 {/if}
             </main>
-            {if ($rightSidebarElements > 0 && $staticpage_pagetitle =='') || ($rightSidebarElements > 0 && $staticpage_pagetitle !='' && $staticpage_custom.show_sidebars != 'false')}
+            {if isset($rightSidebarElements) && ($rightSidebarElements > 0 && (! isset($staticpage_pagetitle) or $staticpage_pagetitle == '')) || isset($rightSidebarElements) && ($rightSidebarElements > 0 && isset($staticpage_pagetitle) and $staticpage_pagetitle !='' && $staticpage_custom.show_sidebars != 'false')}
                 <aside class="col-md-3 RightSideBarContainer">
                     <div id="serendipityRightSideBar" class="RightSideBar">
                         {serendipity_printSidebar side="right"}