EscapeDNComponent

Hi,

I use a display name format of lastname, firstname so I'm trying to use EscapeDNComponent to escape the comma. However, I get an error when the WF executes:

Object Reference not set to an instance of an object

If I use "DisplayName" directly, the WF generates the correct string. 

My customexpression looks like so:

EscapeDNComponent("CN=" + DisplayName)

I'm sure its bombing out at this point. If I remove the CustomExpression and do a simple "CN=" + DisplayName, the correct string is generated (but ofcourse that won't work when provisioning to AD)

Also, I'm trying to use this as part of a function evaluator which constructs the DN then passes it to the sync rule. Is there a limitation that EscapeDNComponent cannot be used inside a function evaluator?

Thanks