Customer and Reseller page display Error and we can not able to create and edit page.

Steps:

1. log in as admin
2. create one tax 
3. create one customer 
4. created tax automatically assign to created customer
5. now delete the above assigned tax.
6. now go to customer grid page and try to create or edit customer/provider and observe.

Bug Description :

when we create tax then it  apply to all customers/providers automatically and when we delete the created tax then it give sql error.

Expected result: 

when we delete the created tax then it  does not give sql erro in customer create and edit page.