Gateway Tag Change Script getPreviousValue() errors?

General Discussion
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1

I’m trying to get the previous value on the tag before it changed and . .
All my attempts to use getPreviousValue().getValue() generate errors

I read through posts like these where getPreviousValue().getValue() is mentioned
change-script-triggered-with-no-reason
gateway-tag-change-script-issue
yet when I try to run getPreviousValue().getValue() in a script I receive the error ‘NoneType’ object has no attribute 'getValue’

Also, looking at getPreviousValue() in the documentation below
Gateway Event Scripts Overview
and when I run getPreviousValue() I see the error ‘getPreviousValue’ is not defined

What is the correct way to get the previous value? Or perhaps I’m overlooking something obvious?

2

It doesn’t exist when initialChange is true. So it is null or None and has no .value property. Either check the initialChange flag or check for None.

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3

That must be the cause of my problem then. I’m triggering the event by saving the script

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