Attempt to index nil with "IsA"?

Hello, I'm trying to make a script that when you hit a part named "Vetro" the part destroys. I'm doing it serverside.

I get the error "Attempt to index nil with "IsA"?" and I don't understand why I can't fix it.

Take note that that's a RemoteEvent, that's why I've put the if statement.

ServerSide script:

if t == "w" then
	    local function vetro(hitted)
			if hitted:IsA("BasePart") and hitted.Name == "Vetro" and hitted.Transparency > 0 then
				hitted:Destroy()
			end
		end
		vetro()
	end

ClientSide script part:

function vetro()
	script.Parent.Event:FireServer("w")
end

I've also tried changing "IsA" with ClassName but still getting an error. Can someone help me please?

if t == "w" then
        local function vetro(hitted)
            if typeof(hitted) == "Instance" and hitted:IsA("BasePart") and hitted.Name == "Vetro" and hitted.Transparency > 0 then
                hitted:Destroy()
            end
        end
        vetro()
    end

I've added typeof() to check if it is an Instance and not a string. May help