I noticed MODx (Evo) does not create a record for the tv value if it is empty for a document (or default is kept). Only if you change it to something, it will create it. As soon as you clear its content, it will delete the record again. (I think this is not documented anywhere

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Now this is a bummer. I want to preprocess some tv values and the content field and store result in another tv. So later I can output this efficiently in a Ditto placeholder.
At first it was working perfectly by using updateTV. Until I noticed this behaviour for empty/defaultvalue TVs. The first time i need to type some bogus into the tv manually just to get the record in there and be able to call $cake->updateTV(..) on it.
Problem summary: The CakeModX api function updateTV will only update existing records. The function setTV will add an entirely new tv not insert a new value record (better call it addTV). Does anyone have a workaround for this?