Resolving Microsoft Identity Manager "sync-rule-validation-parsing-error" error

A couple of weeks back I inherited a Microsoft Identity Manager development environment that wasn’t quite complete. When I performed a sync on a user object I got the following error;  sync-rule-validation-parsing-error

Looking into the error for further details, Details and Stack Trace were both greyed out as shown below.

I looked at the object being exported on the MA and the awaiting export details and found slightly different information. The error was CS to MV to CS synchronization failed 0x8023055a 
Still not a lot to go on. So I looked in the Application Event Log and nothing. Anything in the System Event Log? No, nothing.
So my attention turned to the Export Synchronization Rule. Here is a partial screenshot of the Export Sync Rule. The object (user) in question had been flagged as inactive and the intent appeared to be a clearing of a number of attributes. Sending “” (crude empty/null) to an attribute isn’t very elegant.

I changed each to use the null function. So for export, null() will flow to each of the attributes. I tried the export again and the same error and problem resulted.
Running short on ideas I created a brand new Export Synchronization Rule and replicated the configuration except for the attributes being exported. Then I added one attribute into the rule at a time, tested the export and repeated until I could replicate the error.
I was able to replicate the error once I hit the terminalServer attribute.
*Note: the screenshot below is prior to changing over to flow null() instead of “”.

Sending null() to the terminalServer Active Directory attribute was causing the error. It was at this point I actually just removed that flow rule and continued with other tasks.
Coming back to this later, and thinking it through I understand the error. When dealing with Terminal Services you actually normally manage four attributes that are part of the userParameters attribute. The four attributes that define a users Terminal Services Profile are;

• allowLogon
• terminalServicesHomeDirectory
• terminalServicesProfilePath
• terminalServicesHomeDrive

For a user that has a fully configured set of Terminal Services attributes, sending null() to the terminalServer attribute isn’t going to work.
So, posting this as I couldn’t find any reference to sync-rule-validation-parsing-error or CS to MV to CS synchronization failed 0x8023055a elsewhere and chances are I’ll come across it again, and it’ll probably help someone else too.