## Description <!-- A clear and concise description of the problem with screenshots of the issue, if applicable. What is the behavior you see and what behavior do you expect? (Note: Feature requests should be made by creating a new topic here: https://discourse.paraview.org/c/feature-requests/14). --> The `Convert To Point Cloud` filter crashes when the input is a `vtkPointSet` that is missing a `vtkPoints` object. This is actually an important use cases because when running with a parallel server, it is not uncommon for one of the ranks to have an empty dataset, which could mean that there is no `vtkPoints` object. In this case, the filter should just create an empty `vtkPolyData` with no cells. ## Steps to reproduce <!-- Steps to reproduce the behavior. Include example datafiles and/or state files that demonstrate the behavior. Screenshots may be helpful. --> 1. Connect the ParaView client to a `pvserver` running in an MPI with at least 2 nodes. 2. Open this file: [particles.vtu](/uploads/f9c7373403db3c3658b5797a9831d720/particles.vtu) * Apply 3. Add the `Convert to Point Cloud` filter. Apply. The server will crash. It crashes in [`vtkPoints::ShallowCopy`](https://gitlab.kitware.com/vtk/vtk/-/blob/master/Common/Core/vtkPoints.cxx?ref_type=heads#L246) when trying to copy a source `vtkPoints` that is null. This is being called from [`vtkConvertToPointCloud`](https://gitlab.kitware.com/vtk/vtk/-/blob/master/Filters/Points/vtkConvertToPointCloud.cxx?ref_type=heads#L31), which is checking to see if the input is a `vtkPointSet` but not checking to see if it has points. ## Configuration <!-- Operating system, standalone client, client/server, pvpython, pvbatch --> This happens on pretty much any version of ParaView. I'm pretty sure it dates back to at least 5.10 and still exists in 5.13. * **Operating system and version:** Any * **ParaView executable and version:** <!-- GUI client, pvpython, pvbatch, etc. --> GUI client (and other configurations, too) * **ParaView configuration:** <!-- standalone client, remote server, Catalyst, etc. --> client/server with the server on at least 2 MPI ranks.