Magento2.1.0 showing error Required parameter 'theme_dir' was not passed while saving product in admin

This error appears when you remove a template folder, which is still referenced in the database. The simplest way to fix it is, go to the database, and in table 'theme', find the theme name which does not exist in app/design/frontend/package.

DELETE the reference to the missing theme from the table.

I can confirm that the answer by Vu Anh works. Here's an explanation why this happens when products are saved, although the deleted theme is used nowhere:

After saving a product, the image cache is regenerated for all themes. Each theme can have its own image size formats, defined in etc/view.xml and all of these will be generated.

But instead of looking for the configured themes in all stores, Magento goes through all themes in the theme table.

If you did not properly uninstall a theme and just removed the files, the orphaned entry refers to a nonexistent path and the described exception is thrown.

I have the same error Required parameter 'theme_dir' was not passed. I work with 2.1.0 from the beginning, not with updating. And I have one custom product attribute "style".

The problem occurs when I try to save the new photo in the material. Without the image, the product saved normally.

Fix with commenting the exception under the file:

vendor/magento/framework/view/design/Fallbck/Rule/Simple.php  

It worked for me. But I think it's a hack.