Can you turn a stroke outline into a shape?

I created a fat transparent line with arrowhead. I don’t like how it looks with the overlapping stroke in the arrowhead. I thought, maybe there is a way to turn that outline into a solid shape, so it can be filled. I don’t see such a function.

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Nevermind. I see it’s a feature of OmniGraffle 7 Pro. I’m running version 6. I need to upgrade.