Is this error you are seeing when executing from Designer? I executed following from SquirreL fine against 7.2 Final Teiid.
select cast(null as timestamp) as t from pm1.g1
select convert(null, timestamp) as t from pm1.g1
What query are you executing in Designer, or is this just from a preview? As Ramesh is getting at the error you are seeing is more than likely not directly related to the converion of a null to timestamp. Perhaps there is something in the definition of T where are a source column of type int has been given a runtime type of timestamp.
This sql is written in the Designer.
We use it deploy the VDB to JBoss and execute it.
You can give us a sample test VDB with your issue, we will check this out.
Do you only need the VDB file? Is that enough?
Thanks for your patience.