Type error after asserting an Instance property and using one of the Instance's methods

[someone19204]

In this example code Instance.FindFirstChild later results in type errors when trying to access the part.

--!strict
local part = Instance.new("Part")
assert(part.CanCollide)
if part:FindFirstChild("Part") then print(part) end

[someone19204]

This also seems to happen on children when using one of their methods.