This error indicates that somewhere $modx->addPackage('', $path); is called with an empty first parameter (or a parameter that isn’t a string).
As it is unlikely that this is the case in an established extra, do you call addPackage yourself in one of your snippets?
To find the culprit maybe you can deactivate the snippets one by one (by putting an - before the snippet name; e.g. [[-!mySnippet]]) and check if the error still appears. Or maybe also deactivate the active plugins one by one.
Well, it looks like the name of the package is missing in the $path parameter as well.
With plugins and snippets deactivated I’m not sure what else could cause the error.
Maybe you could also check the system setting extension_packages to see if everything is correct there. And maybe also check the content of the database table modx_extension_packages.