^CMake Error at .*/Modules/ExternalData.cmake:[0-9]+ \(message\):
  No ExternalData_CUSTOM_SCRIPT_RelPathKey is not set to a full path:

   RelPathScript.cmake
Call Stack \(most recent call first\):
  BadCustom4.cmake:[0-9]+ \(ExternalData_Add_Target\)
  CMakeLists.txt:[0-9]+ \(include\)$