Fix reassign cast

Author: swissspidy

features/user.feature

@@ -190,7 +190,7 @@ Feature: Manage WordPress users
       --reassign parameter is invalid. All associated posts will be deleted. Proceed? [y/n]
       """
 
-    When I run `wp user delete bobjones < session_yes`
+    When I try `wp user delete bobjones < session_yes`
     And I run `wp post list --format=count`
     Then STDOUT should be:
       """

src/User_Command.php

@@ -287,7 +287,10 @@ public function delete( $args, $assoc_args ) {
 		 * @var string|null $reassign
 		 */
 		$reassign = Utils\get_flag_value( $assoc_args, 'reassign' );
-		$reassign = (int) $reassign;
+
+		if ( null !== $reassign ) {
+			$reassign = (int) $reassign;
+		}
 
 		if ( $network && $reassign ) {
 			WP_CLI::error( 'Reassigning content to a different user is not supported on multisite.' );