CompositePolyDataMapper2 and QuadricLODActor

Hello all,

I managed to use a QuadricLODActor with a composite mapper but then encountered crashes for example, when zooming out.

It appears that vtkQuadricLODActor::Render will decide whether or not to rebuild LOD. If this is the case then it will call mapper::GetInput.
The issue is that the composite mapper will return NULL here. And the code will crash a bit later when PolyData::GetBounds will be called on NULL.

Is it wrong trying to use a composite mapper with such actor?
Should the actor be patched to call mapper::GetInputDataObject(0, 0) if composite?

I am currently using a more simple vtkLODActor but would like to hear your suggestions.
Thank you

Here is a minimal crashy Python script (tested on VTK8.2.1 and VTK9):

import vtk

composite = vtk.vtkMultiBlockDataSet()
for i in (1, 2):
  sphere = vtk.vtkSphereSource()
  sphere.SetCenter(i, 0., 0.)
  sphere.SetRadius(0.5)

  sphere.Update()
  composite.SetBlock(i, sphere.GetOutput())

mapper = vtk.vtkCompositePolyDataMapper2()
mapper.SetInputDataObject(composite)

# XXX THE CRASH TRIGGER
crash = True
if crash:
  actor = vtk.vtkQuadricLODActor()
else:
  actor = vtk.vtkLODActor()
actor.SetMapper(mapper)

renderer = vtk.vtkRenderer()
renderer.AddActor(actor)

window = vtk.vtkRenderWindow()
window.AddRenderer(renderer)

interactor = vtk.vtkRenderWindowInteractor()
interactor.SetRenderWindow(window)

window.Render()
interactor.Start()