diff --git a/includes/user/UserOptionsManager.php b/includes/user/UserOptionsManager.php
index 55b21231f98..6c640d6f5fa 100644
--- a/includes/user/UserOptionsManager.php
+++ b/includes/user/UserOptionsManager.php
@@ -176,7 +176,7 @@ class UserOptionsManager extends UserOptionsLookup {
 		if ( $flags & self::EXCLUDE_DEFAULTS ) {
 			$defaultOptions = $this->defaultOptionsLookup->getDefaultOptions();
 			foreach ( $options as $option => $value ) {
-				if ( isset( $defaultOptions[$option] )
+				if ( array_key_exists( $option, $defaultOptions )
 					&& $this->isValueEqual( $value, $defaultOptions[$option] )
 				) {
 					unset( $options[$option] );
diff --git a/tests/phpunit/includes/user/UserOptionsManagerTest.php b/tests/phpunit/includes/user/UserOptionsManagerTest.php
index 9754abc7ea7..211dc7204fa 100644
--- a/tests/phpunit/includes/user/UserOptionsManagerTest.php
+++ b/tests/phpunit/includes/user/UserOptionsManagerTest.php
@@ -88,7 +88,6 @@ class UserOptionsManagerTest extends UserOptionsLookupTest {
 		$expected = [
 			// Note that the old, relaxed array_diff-approach considered null equal to false and ""
 			'null_vs_false' => false,
-			'null_vs_string' => '',
 			'language' => 'en',
 			'variant' => 'en',
 			'new_option' => 'new_value',