diff --git a/src/wp-admin/includes/class-wp-list-table.php b/src/wp-admin/includes/class-wp-list-table.php
index b23da4cee8..93a91e420f 100644
--- a/src/wp-admin/includes/class-wp-list-table.php
+++ b/src/wp-admin/includes/class-wp-list-table.php
@@ -345,8 +345,9 @@ class WP_List_Table {
 	 * @access protected
 	 *
 	 * @param string $which The location of the bulk actions: 'top' or 'bottom'.
+	 *                      This is designated as optional for backwards-compatibility.
 	 */
-	protected function bulk_actions( $which ) {
+	protected function bulk_actions( $which = '' ) {
 		if ( is_null( $this->_actions ) ) {
 			$no_new_actions = $this->_actions = $this->get_bulk_actions();
 			/**