Can a Validation rule be used to make a text field required based on a picklist value?

Line Chef david_swedburg
Line Chef
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What I am trying to do is make the Description Part Overwrite field required if the Parts Branch is 102-EquipmentMorris-SUP. For some reason the validation rule I created does not seem to be working and I am wondering if it is because I am using "IsNull" on a text area field.

Below is the Validation I tried but does not seem to work.

If anyone could help me see what I am missing it would be much appreciated.

Thanks,