Groovy to identify deltas in edited cells in a form

Summary:

I'm new to Groovy and in one implementation of Planning I need to create a rule that can identify not only which cells were modified, but what was the "delta" of that modification, and perform some other activities on that difference.

My "AI" is advising me the following code, but I don't find a cell.getOldData() method in none of the Groovy references as the rule is not Validated, so I assume this is the typical AI-llucination, but decided to ask you experts to confirm, and if confirmed, suggest me a different alternative to get that "delta" using Groovy.