I'm unable to reproduce this error. Just to be clear, is it happening every time you press F, or just occasionally/rarely?
Only thing that I can think of is that you've renamed base game packages, maybe? It's looking for something in the package "com.fs.graphics", so if you renamed that or it's not there, you'd get this error.
Try replacing the jar file in Officer Extension/jars with the attached one, it changes the way the mod looks for that object.
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