diff --git a/administrator/components/com_banners/src/Model/ClientsModel.php b/administrator/components/com_banners/src/Model/ClientsModel.php
index da569440e06fc..84e35a2bf7b03 100644
--- a/administrator/components/com_banners/src/Model/ClientsModel.php
+++ b/administrator/components/com_banners/src/Model/ClientsModel.php
@@ -162,7 +162,7 @@ protected function getListQuery()
 		);
 
 		// Filter by search in title
-		if ($search = trim($this->getState('filter.search')))
+		if ($search = trim($this->getState('filter.search', '')))
 		{
 			if (stripos($search, 'id:') === 0)
 			{
diff --git a/administrator/components/com_config/src/Controller/DisplayController.php b/administrator/components/com_config/src/Controller/DisplayController.php
index 7a5b66263169a..2ed6a6f030c14 100644
--- a/administrator/components/com_config/src/Controller/DisplayController.php
+++ b/administrator/components/com_config/src/Controller/DisplayController.php
@@ -47,7 +47,7 @@ class DisplayController extends BaseController
 	 */
 	public function display($cachable = false, $urlparams = array())
 	{
-		$component = $this->input->get('component');
+		$component = $this->input->get('component', '');
 
 		// Make sure com_joomlaupdate and com_privacy can only be accessed by SuperUser
 		if (in_array(strtolower($component), array('com_joomlaupdate', 'com_privacy'))
diff --git a/administrator/components/com_fields/src/Plugin/FieldsPlugin.php b/administrator/components/com_fields/src/Plugin/FieldsPlugin.php
index b72b54e3853e7..2c674e5a06cef 100644
--- a/administrator/components/com_fields/src/Plugin/FieldsPlugin.php
+++ b/administrator/components/com_fields/src/Plugin/FieldsPlugin.php
@@ -194,10 +194,10 @@ public function onCustomFieldsPrepareDom($field, \DOMElement $parent, Form $form
 		$node->setAttribute('name', $field->name);
 		$node->setAttribute('type', $field->type);
 		$node->setAttribute('label', $field->label);
-		$node->setAttribute('labelclass', $field->params->get('label_class'));
+		$node->setAttribute('labelclass', $field->params->get('label_class', ''));
 		$node->setAttribute('description', $field->description);
-		$node->setAttribute('class', $field->params->get('class'));
-		$node->setAttribute('hint', $field->params->get('hint'));
+		$node->setAttribute('class', $field->params->get('class', ''));
+		$node->setAttribute('hint', $field->params->get('hint', ''));
 		$node->setAttribute('required', $field->required ? 'true' : 'false');
 
 		if ($field->default_value !== '')
diff --git a/administrator/components/com_finder/src/Indexer/Query.php b/administrator/components/com_finder/src/Indexer/Query.php
index 5a5a652ac1cb3..952dddb0cc169 100644
--- a/administrator/components/com_finder/src/Indexer/Query.php
+++ b/administrator/components/com_finder/src/Indexer/Query.php
@@ -750,6 +750,11 @@ protected function processDates($date1, $date2, $when1, $when2)
 	 */
 	protected function processString($input, $lang, $mode)
 	{
+		if ($input === null)
+		{
+			$input = '';
+		}
+
 		// Clean up the input string.
 		$input  = html_entity_decode($input, ENT_QUOTES, 'UTF-8');
 		$input  = StringHelper::strtolower($input);
diff --git a/administrator/components/com_mails/src/Model/TemplateModel.php b/administrator/components/com_mails/src/Model/TemplateModel.php
index ed81192e4fe48..b8f27589b63df 100644
--- a/administrator/components/com_mails/src/Model/TemplateModel.php
+++ b/administrator/components/com_mails/src/Model/TemplateModel.php
@@ -114,7 +114,7 @@ public function getForm($data = array(), $loadData = true)
 			$form->removeField('copyto', 'params');
 		}
 
-		if (!trim($params->get('attachment_folder')))
+		if (!trim($params->get('attachment_folder', '')))
 		{
 			$form->removeField('attachments');
 
diff --git a/administrator/components/com_menus/tmpl/items/default_batch_body.php b/administrator/components/com_menus/tmpl/items/default_batch_body.php
index a329cd86e2510..acb8b8e97b71f 100644
--- a/administrator/components/com_menus/tmpl/items/default_batch_body.php
+++ b/administrator/components/com_menus/tmpl/items/default_batch_body.php
@@ -20,7 +20,7 @@
 ];
 $published = (int) $this->state->get('filter.published');
 $clientId  = (int) $this->state->get('filter.client_id');
-$menuType  = Factory::getApplication()->getUserState('com_menus.items.menutype');
+$menuType  = Factory::getApplication()->getUserState('com_menus.items.menutype', '');
 
 if ($clientId == 1)
 {
diff --git a/administrator/components/com_menus/tmpl/items/default_batch_footer.php b/administrator/components/com_menus/tmpl/items/default_batch_footer.php
index 0216c8c0e1bfa..e58750f8d495a 100644
--- a/administrator/components/com_menus/tmpl/items/default_batch_footer.php
+++ b/administrator/components/com_menus/tmpl/items/default_batch_footer.php
@@ -13,7 +13,7 @@
 
 $published = $this->state->get('filter.published');
 $clientId  = $this->state->get('filter.client_id');
-$menuType = Factory::getApplication()->getUserState('com_menus.items.menutype');
+$menuType = Factory::getApplication()->getUserState('com_menus.items.menutype', '');
 ?>
 <button type="button" class="btn btn-secondary" onclick="document.getElementById('batch-menu-id').value='';document.getElementById('batch-access').value='';document.getElementById('batch-language-id').value=''" data-bs-dismiss="modal">
 	<?php echo Text::_('JCANCEL'); ?>
diff --git a/administrator/components/com_templates/src/View/Template/HtmlView.php b/administrator/components/com_templates/src/View/Template/HtmlView.php
index 304646efaee61..e8eeca9291219 100644
--- a/administrator/components/com_templates/src/View/Template/HtmlView.php
+++ b/administrator/components/com_templates/src/View/Template/HtmlView.php
@@ -148,7 +148,7 @@ public function display($tpl = null)
 	{
 		$app            = Factory::getApplication();
 		$this->file     = $app->input->get('file');
-		$this->fileName = InputFilter::getInstance()->clean(base64_decode($this->file), 'string');
+		$this->fileName = InputFilter::getInstance()->clean(base64_decode($this->file ?? ''), 'string');
 		$explodeArray   = explode('.', $this->fileName);
 		$ext            = end($explodeArray);
 		$this->files    = $this->get('Files');