diff --git a/administrator/components/com_content/models/articles.php b/administrator/components/com_content/models/articles.php
index 0d28a2ae90d5c..6a5aa3c4bc62e 100644
--- a/administrator/components/com_content/models/articles.php
+++ b/administrator/components/com_content/models/articles.php
@@ -267,12 +267,13 @@ protected function getListQuery()
 		}
 
 		// Filter by categories and by level
-		$categoryId = $this->getState('filter.category_id');
+		$categoryId = $this->getState('filter.category_id', array());
 		$level = $this->getState('filter.level');
 
-		$categoryId = $categoryId && !is_array($categoryId)
-			? array($categoryId)
-			: $categoryId;
+		if (!is_array($categoryId))
+		{
+			$categoryId = $categoryId ? array($categoryId) : array();
+		}
 
 		// Case: Using both categories filter and by level filter
 		if (count($categoryId))
diff --git a/libraries/src/Updater/Adapter/CollectionAdapter.php b/libraries/src/Updater/Adapter/CollectionAdapter.php
index 45e0f1afbb18e..9313bf52613ed 100644
--- a/libraries/src/Updater/Adapter/CollectionAdapter.php
+++ b/libraries/src/Updater/Adapter/CollectionAdapter.php
@@ -50,16 +50,18 @@ class CollectionAdapter extends UpdateAdapter
 	protected $pop_parent = 0;
 
 	/**
-	 * @var array A list of discovered update sites
+	 * A list of discovered update sites
+	 *
+	 * @var  array
 	 */
-	protected $update_sites;
+	protected $update_sites = array();
 
 	/**
 	 * A list of discovered updates
 	 *
-	 * @var array
+	 * @var  array
 	 */
-	protected $updates;
+	protected $updates = array();
 
 	/**
 	 * Gets the reference to the current direct parent
diff --git a/modules/mod_tags_similar/helper.php b/modules/mod_tags_similar/helper.php
index 82ee15f6ad115..f4b1686c445be 100644
--- a/modules/mod_tags_similar/helper.php
+++ b/modules/mod_tags_similar/helper.php
@@ -23,7 +23,7 @@ abstract class ModTagssimilarHelper
 	 *
 	 * @param   Registry  &$params  Module parameters
 	 *
-	 * @return  mixed  Results array / null
+	 * @return  array
 	 */
 	public static function getList(&$params)
 	{
@@ -35,7 +35,7 @@ public static function getList(&$params)
 		// This module does not apply to list views in general at this point.
 		if ($option === 'com_tags' || $view === 'category' || $option === 'com_users')
 		{
-			return;
+			return array();
 		}
 
 		$db         = JFactory::getDbo();
@@ -54,7 +54,7 @@ public static function getList(&$params)
 
 		if (!$tagsToMatch || $tagsToMatch === null)
 		{
-			return;
+			return array();
 		}
 
 		$tagCount = substr_count($tagsToMatch, ',') + 1;