Mass Update To be Emailed field on Invoices throws an error: You must enter a valid email address in order to email the transaction

1. As Administrator navigate to Lists > Mass Update > Mass Updates > General Updates. 
2. Click Invoice.
3. Enter all criteria.
4. Navigate to Mass Update Fields tab.
5. In the Apply checkbox put a check mark next to the To Be E-mailed field.
6. In the Value column, put a check mark next to the To Be E-mailed field.
7. Click Preview button.
8. Click Perform Update.

User got an error message: You must enter a valid email address in order to email the transaction.

The error is being caused by one or more Invoices with no Email value in the Invoice record > Communication tab > Messages subtab > To be emailed.