Just did a clean build of Paraview off of commit deade123.
CMake sequence on Ubuntu 18.04:
$ cmake -DPARAVIEW_BUILD_TESTING=ON -DPARAVIEW_USE_PYTHON=ON ../ -G Ninja
Next, I tried "Sources -> Alphabetical -> SplineSource". I tried to add a control point with ctrl-P, as is in the directions, and obtained the following error:
The error log and a screenshot is attached: