Symptoms

Using an email event, customer was assigning a datafield as the "CC" address. This datafield could have zero or more email addresses. Whenever the datafield had no value, the k2 process would error out with the error, "The email address, Null or Empty, does not meet the requirements."
 

Diagnoses

This is a known issue in K2, with a workaround available.
 

Resolution

Workaround:
Change the code behind the mail event to handle the Null value and comment out the Exception.

Ie:

if (!string.IsNullOrEmpty(K2.Configuration.To))
{
stringi] arrto = K2.Configuration.To.Split('')
foreach (string to in arrto)
{
if (!string.IsNullOrEmpty(to)) ---- NOTE THE !
{
// throw new ArgumentException("The email address, Null or Empty, does not meet the requirements.")
//}

This can be done to the needed fields like TO, CC, BCC