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 6e1f087..31e4fa3 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 @@ protected function opRegex($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') {
       $operator = "IS NULL";
     }
diff --git a/core/modules/views/lib/Drupal/views/Plugin/views/filter/GroupByNumeric.php b/core/modules/views/lib/Drupal/views/Plugin/views/filter/GroupByNumeric.php
index cedae6d..f1069af 100644
--- a/core/modules/views/lib/Drupal/views/Plugin/views/filter/GroupByNumeric.php
+++ b/core/modules/views/lib/Drupal/views/Plugin/views/filter/GroupByNumeric.php
@@ -44,7 +44,7 @@ protected function opSimple($field) {
     $this->query->addHavingExpression($this->options['group'], "$field $this->operator $placeholder", array($placeholder => $this->value['value']));
   }
 
-  function op_empty($field) {
+  protected function opEmpty($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 ccfac66..537e6c8 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' => 'opEmpty',
           'short' => t('empty'),
           'values' => 0,
         ),
         'not empty' => array(
           'title' => t('Is not empty (NOT NULL)'),
-          'method' => 'op_empty',
+          'method' => 'opEmpty',
           'short' => t('not empty'),
           'values' => 0,
         ),
@@ -387,7 +387,7 @@ protected function opSimple() {
     $this->query->addWhere($this->options['group'], "$this->tableAlias.$this->realField", array_values($this->value), $this->operator);
   }
 
-  function op_empty() {
+  protected function opEmpty() {
     $this->ensureMyTable();
     if ($this->operator == 'empty') {
       $operator = "IS NULL";
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 797df56..e174824 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' => 'opEmpty',
           'short' => t('empty'),
           'values' => 0,
         ),
         'not empty' => array(
           'title' => t('Is not empty (NOT NULL)'),
-          'method' => 'op_empty',
+          'method' => 'opEmpty',
           '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 99896e4..8f8eab1 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() {
       $operators += array(
         'empty' => array(
           'title' => t('Is empty (NULL)'),
-          'method' => 'op_empty',
+          'method' => 'opEmpty',
           'short' => t('empty'),
           'values' => 0,
         ),
         'not empty' => array(
           'title' => t('Is not empty (NOT NULL)'),
-          'method' => 'op_empty',
+          'method' => 'opEmpty',
           'short' => t('not empty'),
           'values' => 0,
         ),
@@ -264,7 +264,7 @@ protected function opSimple($field) {
     $this->query->addWhere($this->options['group'], $field, $this->value['value'], $this->operator);
   }
 
-  function op_empty($field) {
+  protected function opEmpty($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 c392876..28d6da4 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() {
       $operators += array(
         'empty' => array(
           'title' => t('Is empty (NULL)'),
-          'method' => 'op_empty',
+          'method' => 'opEmpty',
           'short' => t('empty'),
           'values' => 0,
         ),
         'not empty' => array(
           'title' => t('Is not empty (NOT NULL)'),
-          'method' => 'op_empty',
+          'method' => 'opEmpty',
           'short' => t('not empty'),
           'values' => 0,
         ),
@@ -335,7 +335,7 @@ protected function opRegex($field) {
     $this->query->addWhere($this->options['group'], $field, $this->value, 'RLIKE');
   }
 
-  function op_empty($field) {
+  protected function opEmpty($field) {
     if ($this->operator == 'empty') {
       $operator = "IS NULL";
     }