Which type of exception will this trigger cause?

A lead object has a custom field Prior_Email__c.

The following trigger is intended to copy the current Email into the Prior_Email__c field any time the Email field is changed:

Which type of exception will this trigger cause?
A . A null reference exception
B . A compile time exception
C . A DML exception
D . A limit exception when doing a bulk update

View Answer

Answer: C