diff --git a/wp-includes/user.php b/wp-includes/user.php
index d0b760986c..8bc44ae233 100644
--- a/wp-includes/user.php
+++ b/wp-includes/user.php
@@ -1005,12 +1005,12 @@ function count_users( $strategy = 'time', $site_id = null ) {
  * @global string  $user_url      The url in the user's profile
  * @global string  $user_identity The display name of the user
  *
- * @param int $for_user_id Optional. User ID to set up global data.
+ * @param int $for_user_id Optional. Default 0. User ID to set up global data.
  */
-function setup_userdata( $for_user_id = '' ) {
+function setup_userdata( $for_user_id = 0 ) {
 	global $user_login, $userdata, $user_level, $user_ID, $user_email, $user_url, $user_identity;
 
-	if ( '' == $for_user_id ) {
+	if ( ! $for_user_id ) {
 		$for_user_id = get_current_user_id();
 	}
 	$user = get_userdata( $for_user_id );
diff --git a/wp-includes/version.php b/wp-includes/version.php
index beb08a0cb9..bc0c4a3ac9 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.1-beta1-44602';
+$wp_version = '5.1-beta1-44603';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.