diff --git a/backup/util/structure/base_nested_element.class.php b/backup/util/structure/base_nested_element.class.php
index b48defc823533..0067410a21026 100644
--- a/backup/util/structure/base_nested_element.class.php
+++ b/backup/util/structure/base_nested_element.class.php
@@ -164,8 +164,8 @@ public function add_final_elements($final_elements) {
     }
 
     public function add_child($element) {
-        if (!($element instanceof base_nested_element)) { // parameter must be a base_nested_element
-            if (!$found = get_class($element)) {
+        if (!is_object($element) || !($element instanceof base_nested_element)) { // parameter must be a base_nested_element
+            if (!is_object($element) || !($found = get_class($element))) {
                 $found = 'non object';
             }
             throw new base_element_struct_exception('nestedelementincorrect', $found);
diff --git a/cache/disabledlib.php b/cache/disabledlib.php
index 3a83d1fd64377..2bcc1caf8ad0f 100644
--- a/cache/disabledlib.php
+++ b/cache/disabledlib.php
@@ -125,9 +125,10 @@ public function delete_many(array $keys, $recurse = true) {
      * Checks if the cache has the requested key.
      *
      * @param int|string $key Unused.
+     * @param bool $tryloadifpossible Unused.
      * @return bool
      */
-    public function has($key) {
+    public function has($key, $tryloadifpossible = false) {
         return false;
     }
 
diff --git a/filter/urltolink/filter.php b/filter/urltolink/filter.php
index 211e149e8376d..b8a333e2952f8 100644
--- a/filter/urltolink/filter.php
+++ b/filter/urltolink/filter.php
@@ -75,6 +75,7 @@ protected function convert_urls_into_links(&$text) {
         //<a href="blah">
         $filterignoretagsopen  = array('<a\s[^>]+?>', '<span[^>]+?class="nolink"[^>]*?>');
         $filterignoretagsclose = array('</a>', '</span>');
+        $ignoretags = [];
         filter_save_ignore_tags($text,$filterignoretagsopen,$filterignoretagsclose,$ignoretags);
 
         // Check if we support unicode modifiers in regular expressions. Cache it.
diff --git a/lib/navigationlib.php b/lib/navigationlib.php
index 280b1191be8e7..efb92a95513b6 100644
--- a/lib/navigationlib.php
+++ b/lib/navigationlib.php
@@ -843,7 +843,7 @@ public function action() {
  * @copyright 2010 Sam Hemelryk
  * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
-class navigation_node_collection implements IteratorAggregate {
+class navigation_node_collection implements IteratorAggregate, Countable {
     /**
      * A multidimensional array to where the first key is the type and the second
      * key is the nodes key.
diff --git a/lib/outputcomponents.php b/lib/outputcomponents.php
index e237ba5a9aad0..fac5c37ab8e8f 100644
--- a/lib/outputcomponents.php
+++ b/lib/outputcomponents.php
@@ -2640,7 +2640,7 @@ class html_table {
      * $row2->cells = array($cell2, $cell3);
      * $t->data = array($row1, $row2);
      */
-    public $data;
+    public $data = [];
 
     /**
      * @deprecated since Moodle 2.0. Styling should be in the CSS.
diff --git a/lib/phpunit/classes/base_testcase.php b/lib/phpunit/classes/base_testcase.php
index 231ce1f419859..54eb63fa7ed31 100644
--- a/lib/phpunit/classes/base_testcase.php
+++ b/lib/phpunit/classes/base_testcase.php
@@ -73,7 +73,7 @@ public static function assertTag($matcher, $actual, $message = '', $ishtml = tru
     public static function assertNotTag($matcher, $actual, $message = '', $ishtml = true) {
         $dom = PHPUnit_Util_XML::load($actual, $ishtml);
         $tags = self::findNodes($dom, $matcher, $ishtml);
-        $matched = count($tags) > 0 && $tags[0] instanceof DOMNode;
+        $matched = (is_array($tags) && count($tags) > 0) && $tags[0] instanceof DOMNode;
         self::assertFalse($matched, $message);
     }
 
diff --git a/user/tests/userlib_test.php b/user/tests/userlib_test.php
index a5a68620db3f4..0168929fcc2a1 100644
--- a/user/tests/userlib_test.php
+++ b/user/tests/userlib_test.php
@@ -887,8 +887,8 @@ public function test_user_get_participants() {
         // the group and has the name 'searchforthis' and has also accessed the course in the last day.
         $userset = user_get_participants($course->id, $group->id, $accesssince + 1, $roleids['student'], 0, -1, 'searchforthis');
 
-        $this->assertEquals(1, sizeof($userset));
         $this->assertEquals($student1->id, $userset->current()->id);
+        $this->assertEquals(1, iterator_count($userset));
     }
 
     /**