I want to make the state/province field required on a lead when a user tries to convert the lead to an account. The state field is not required when the lead is created as the user may not know the state at this point.  When the user is ready to convert a lead the state field needs to be known and populated.  The issue is how to make it required only on the conversion and not on the save. I have thought about validations rules, workflow rules and possibly a trigger.  Though I encounter the problem of the required state error occurs on the save not on the conversion.