Hello,
I don't know if this has been reported earlier or not but I am posting this bug here as we found this in nopCommerce 4.10
Steps to reproduce:
1. Go to, Catalog -> Attributes -> Specification attributes in nopCommerce admin. For example, http://admin-demo.nopcommerce.com/Admin/SpecificationAttribute/Edit/5
2. Click on edit for any specification attribute that have option values
3. Go to options tab
4. Delete any option
You will see that option has been deleted but still an ajax loader shows in top right corner of your browser window. This issue is due to null value.
I hope this information is sufficient to debug and fix this issue.
Thank you,
Atul