diff -r c7c34916027a -r 177826044cd9 wp/wp-admin/network/edit.php
--- a/wp/wp-admin/network/edit.php	Mon Oct 14 18:06:33 2019 +0200
+++ b/wp/wp-admin/network/edit.php	Mon Oct 14 18:28:13 2019 +0200
@@ -10,7 +10,9 @@
 /** Load WordPress Administration Bootstrap */
 require_once( dirname( __FILE__ ) . '/admin.php' );
 
-if ( empty( $_GET['action'] ) ) {
+$action = ( isset( $_GET['action'] ) ) ? $_GET['action'] : '';
+
+if ( empty( $action ) ) {
 	wp_redirect( network_admin_url() );
 	exit;
 }
@@ -28,12 +30,12 @@
 /**
  * Fires the requested handler action.
  *
- * The dynamic portion of the hook name, `$_GET['action']`, refers to the name
- * of the requested action.
+ * The dynamic portion of the hook name, `$action`, refers to the name
+ * of the requested action derived from the `GET` request.
  *
  * @since 3.1.0
  */
-do_action( 'network_admin_edit_' . $_GET['action'] );
+do_action( "network_admin_edit_{$action}" );
 
 wp_redirect( network_admin_url() );
 exit();