^CMake Error at .*/Modules/ExternalData.cmake:[0-9]+ \(message\):
  No ExternalData_CUSTOM_SCRIPT_MissingKey is set for URL template:

   ExternalDataCustomScript://MissingKey/%\(algo\)/%\(hash\)
Call Stack \(most recent call first\):
  BadCustom3.cmake:[0-9]+ \(ExternalData_Add_Target\)
  CMakeLists.txt:[0-9]+ \(include\)$