Warning about update error

Hi there,

when I click the link on details about a new version, I receive the following warning in my WP-backend:

Attempt to assign property ‘external’ of non-object in /homepages/15/XXXXXXXXXXX/htdocs/clickandbuilds/XXXXXXXXX/wp-admin/includes/plugin-install.php on line 222

Since I do not want to screw my site, I do not dare to update your plugin. Can you please help and advise as to how I shall proceed to update your plugin safely.

Thanks and beste regards,

Thomas