LinearInterpolation handles collect(x) but not CubicSplineInterplation

CubicSplineInterpolation does not handle collect(), Yet LinearInterpolation does --- see minimal example below. Any suggestions on how to address this?

```using Interpolations
x = collect(1:0.1:5)
y = rand(length(x))
itp1 = LinearInterpolation(x, y; extrapolation_bc=Flat())
@show itp1(4)
@show itp1(6)
itp2 = CubicSplineInterpolation(x, y; extrapolation_bc=Flat())
@show itp2(4)
@show itp2(6)
```