Mandatory job number turned on

Is there possible to set up in the system so that the completion of the job number field is mandatory?

We have many jobs and cost centres/ departments. It would be great that when entering both sales and purchase invoices, this field has to be completed, so that when we run costing reports by job, we can review numbers (for example costs or profitability), by job. 

Attached is an example of a General Ledger account in which some job numbers are entered and some are not.

Appreciate some help.

Thanks in advance.

STan3