^CMake Error at .*/Modules/ExternalData.cmake:[0-9]+ \(message\):
  Bad ExternalDataCustomScript key '0BadKey' in URL template:

   ExternalDataCustomScript://0BadKey/%\(algo\)/%\(hash\)

  The key must be a valid C identifier.
Call Stack \(most recent call first\):
  BadCustom1.cmake:[0-9]+ \(ExternalData_Add_Target\)
  CMakeLists.txt:[0-9]+ \(include\)$
