Billing Document with zero price

Hi Friends,

The scenario is as

Sometimes, the user updates the price in billing document, then some manual conditions are not been updated. So sometimes, the basic price of the material becomes zero and user saves the document with zero base price.

My question is

How to avoid it by giving some pop -up message or information that the base price in document is zero.

Or is it require to have some customization.

Kindly help in this regard

Thanks in advance

Shailesh Choudhari