Writing a reference for someone. Weaknesses?

[purplepeoniesx]

I'm writing a reference for someone I manage. It asks for his weaknesses, but honestly? He's the best worker I've ever had. I actually aspire to be more like him and I genuinely can't think of anything significant enough to put on this reference. What do I write?

Exactly what you've just said OP

That he is leaving?

Be very careful. If he doesn't get the job because of a 'weakness' you have exposed you could find yourself personally on the wrong end of a lawsuit.
I'd put something like "None observed" even if they were the most incompetent slacker.

Agree just put along the lines of what you said in your OP.