How to use the vtkCameraInterpolator

In the example provided at https://examples.vtk.org/site/Cxx/Rendering/InterpolateCamera/,
I replaced interpolator->SetInterpolationTypeToSpline(); with interpolator->SetInterpolationTypeToLinear(); in the code.

However, after making this change, no actors appeared on the screen.
I’m curious about the reason behind this issue.