Bugs in script to populate an empty attribute field

Here is a copy of my script.

Attachment 26766

I am attempting to populate a blank field (Veg_Height) in my shapefile attribute table with text of my own choosing depending on the value in field Class_name.

e.g. if Class_name = "Grass", change the blank Veg_Height field to "Short", if Class_name = "Trees", change the blank Veg_Height field to "Tall" etc.

Unfortunately, at the moment, I keep getting errors when I try to run this in model builder. Can anyone suggest any changes I could make?

Thanks :)

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