Portal 2 Compile Error

I tried making a cube_dropper in Portal 2 and I get an error when compiling. I am not sure if it is something that should be worried about because the map works fine, but what is this error and how do you fix it (if it matters):

ConVarRef gpu_level doesn't point to an existing ConVar

https://developer.valvesoftware.com/wiki/Dropper_%28Portal_2%29 Did you try this?

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Yes, that is exactly what I used. So I will just assume the compile thing is normal, because everything does work fine.