diff --git a/wp-includes/class-wp-comment-query.php b/wp-includes/class-wp-comment-query.php
index f35354c76c..a592fdb687 100644
--- a/wp-includes/class-wp-comment-query.php
+++ b/wp-includes/class-wp-comment-query.php
@@ -801,7 +801,7 @@ class WP_Comment_Query {
 		}
 
 		// Falsey search strings are ignored.
-		if ( strlen( $this->query_vars['search'] ) ) {
+		if ( isset( $this->query_vars['search'] ) && strlen( $this->query_vars['search'] ) ) {
 			$search_sql = $this->get_search_sql(
 				$this->query_vars['search'],
 				array( 'comment_author', 'comment_author_email', 'comment_author_url', 'comment_author_IP', 'comment_content' )
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 1813e1b684..bbea4f8dcd 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9-alpha-51805';
+$wp_version = '5.9-alpha-51806';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.