"Call to a member function xyz() on a non-object" when ommiting ext_name in acp_extensions.php

Fatal error: Call to a member function validate_enable() on a non-object in ...\includes\acp\acp_extensions.php on line 86

One of the translators got this error, I then had a look at the source code and found that the $md_manager is only created, when an ext_name is given. However the object is used later without any previous checking.

Basically the actions: details, enable and enable_pre should check for existance of the object. So:

if (!$md_manager->validate_enable())

should be:

if (!isset($md_manager) || !$md_manager->validate_enable())