diff --git a/core/modules/views/lib/Drupal/views/Plugin/views/filter/Combine.php b/core/modules/views/lib/Drupal/views/Plugin/views/filter/Combine.php
index bdf71f4..8968a1d 100644
--- a/core/modules/views/lib/Drupal/views/Plugin/views/filter/Combine.php
+++ b/core/modules/views/lib/Drupal/views/Plugin/views/filter/Combine.php
@@ -131,7 +131,7 @@ function op_regex($expression) {
     $this->query->add_where_expression($this->options['group'], "$expression RLIKE $placeholder", array($placeholder => $this->value));
   }
 
-  function op_empty($expression) {
+  protected function opEmpty($expression) {
     if ($this->operator == 'empty') {
       $operator = "IS NULL";
     }
diff --git a/core/modules/views/lib/Drupal/views/Plugin/views/filter/GroupByNumeric.php b/core/modules/views/lib/Drupal/views/Plugin/views/filter/GroupByNumeric.php
index 1454bc0..e9d2bcc 100644
--- a/core/modules/views/lib/Drupal/views/Plugin/views/filter/GroupByNumeric.php
+++ b/core/modules/views/lib/Drupal/views/Plugin/views/filter/GroupByNumeric.php
@@ -44,7 +44,7 @@ function op_simple($field) {
     $this->query->addHavingExpression($this->options['group'], "$field $this->operator $placeholder", array($placeholder => $this->value['value']));
   }
 
-  function op_empty($field) {
+  protected function addEmpty($field) {
     if ($this->operator == 'empty') {
       $operator = "IS NULL";
     }
diff --git a/core/modules/views/lib/Drupal/views/Plugin/views/filter/InOperator.php b/core/modules/views/lib/Drupal/views/Plugin/views/filter/InOperator.php
index eaf564c..f9894db 100644
--- a/core/modules/views/lib/Drupal/views/Plugin/views/filter/InOperator.php
+++ b/core/modules/views/lib/Drupal/views/Plugin/views/filter/InOperator.php
@@ -125,13 +125,13 @@ function operators() {
       $operators += array(
         'empty' => array(
           'title' => t('Is empty (NULL)'),
-          'method' => 'op_empty',
+          'method' => 'addEmpty',
           'short' => t('empty'),
           'values' => 0,
         ),
         'not empty' => array(
           'title' => t('Is not empty (NOT NULL)'),
-          'method' => 'op_empty',
+          'method' => 'addEmpty',
           'short' => t('not empty'),
           'values' => 0,
         ),
diff --git a/core/modules/views/lib/Drupal/views/Plugin/views/filter/ManyToOne.php b/core/modules/views/lib/Drupal/views/Plugin/views/filter/ManyToOne.php
index 1f3a672..4e94ef8 100644
--- a/core/modules/views/lib/Drupal/views/Plugin/views/filter/ManyToOne.php
+++ b/core/modules/views/lib/Drupal/views/Plugin/views/filter/ManyToOne.php
@@ -91,13 +91,13 @@ function operators() {
       $operators += array(
         'empty' => array(
           'title' => t('Is empty (NULL)'),
-          'method' => 'op_empty',
+          'method' => 'addEmpty',
           'short' => t('empty'),
           'values' => 0,
         ),
         'not empty' => array(
           'title' => t('Is not empty (NOT NULL)'),
-          'method' => 'op_empty',
+          'method' => 'addEmpty',
           'short' => t('not empty'),
           'values' => 0,
         ),
diff --git a/core/modules/views/lib/Drupal/views/Plugin/views/filter/Numeric.php b/core/modules/views/lib/Drupal/views/Plugin/views/filter/Numeric.php
index c9d5389..c26113e 100644
--- a/core/modules/views/lib/Drupal/views/Plugin/views/filter/Numeric.php
+++ b/core/modules/views/lib/Drupal/views/Plugin/views/filter/Numeric.php
@@ -92,13 +92,13 @@ function operators() {
       $operators += array(
         'empty' => array(
           'title' => t('Is empty (NULL)'),
-          'method' => 'op_empty',
+          'method' => 'addEmpty',
           'short' => t('empty'),
           'values' => 0,
         ),
         'not empty' => array(
           'title' => t('Is not empty (NOT NULL)'),
-          'method' => 'op_empty',
+          'method' => 'addEmpty',
           'short' => t('not empty'),
           'values' => 0,
         ),
@@ -264,7 +264,7 @@ function op_simple($field) {
     $this->query->add_where($this->options['group'], $field, $this->value['value'], $this->operator);
   }
 
-  function op_empty($field) {
+  protected function addEmpty($field) {
     if ($this->operator == 'empty') {
       $operator = "IS NULL";
     }
diff --git a/core/modules/views/lib/Drupal/views/Plugin/views/filter/String.php b/core/modules/views/lib/Drupal/views/Plugin/views/filter/String.php
index c71e14b..fb01de8 100644
--- a/core/modules/views/lib/Drupal/views/Plugin/views/filter/String.php
+++ b/core/modules/views/lib/Drupal/views/Plugin/views/filter/String.php
@@ -116,13 +116,13 @@ function operators() {
       $operators += array(
         'empty' => array(
           'title' => t('Is empty (NULL)'),
-          'method' => 'op_empty',
+          'method' => 'addEmpty',
           'short' => t('empty'),
           'values' => 0,
         ),
         'not empty' => array(
           'title' => t('Is not empty (NOT NULL)'),
-          'method' => 'op_empty',
+          'method' => 'addEmpty',
           'short' => t('not empty'),
           'values' => 0,
         ),
@@ -335,7 +335,7 @@ function op_regex($field) {
     $this->query->add_where($this->options['group'], $field, $this->value, 'RLIKE');
   }
 
-  function op_empty($field) {
+  protected function addEmpty($field) {
     if ($this->operator == 'empty') {
       $operator = "IS NULL";
     }