Magento 2 - Unable to load theme by specified key

[ACmag]

Hello,

I am in the process of upgrading a website from Magento 1.9.2.2 to Magento 2.2.5.

I managed to use the Data Migration Tool and all data appears to have migrated successfully, although I am getting the error below in exception.log.

main.CRITICAL: Unable to load theme by specified key: '' {"exception":"[object] (LogicException(code: 0): Unable to load theme by specified key: '' at /home/anglersc/development.anglerscorner.co.uk/vendor/magento/framework/View/Design/Theme/FlyweightFactory.php:69)"} []

Are there any kind guru's out there that can point me in the right direction to resolve this?

Thanks in advance

[Sunil Patel]

Hello,

maybe in core_config_data contain wrong active theme. 

try to find 

select * from core_config_data  where path like '%theme%';

and check that theme exist into theme table if not then try to change theme id and check it

[ACmag]

Hello,

Thank you for the reply, I tried your suggestion but sadly it was not the cause.

With a bit more digging around I believe the cause was a random empty row in design_change, double checking this in Magento I could see it and deleted it.

Since doing so and refreshing Magento I haven't seen the error, so fingers crossed that it is sorted

[Sunil Patel]

Hello @ACmag

may be wrong theme assigned for category and product please check it