Ticket #43113: class-wp-customize-nav-menu-item-setting.diff

wp-includes/customize/class-wp-customize-nav-menu-item-setting.php

@@ -254 +254 @@
                         $value['type_label'] = $this->get_type_label( (object) $value );
                 }
 
+                if ( ! empty( $value['classes'] ) && ! is_array( $value['classes'] )) {
+                        $value['classes'] = explode( ' ' , $value['classes'] );
+                }
+
                 return $value;
         }