ExternalProject does not allow NOT to init all the submodules
This issue was created automatically from an original Mantis Issue. Further discussion may take place here.
GIT_SUBMODULES argument, it is possible to initialize and update only a subset of modules, but it is not possible to skip all of them
GIT_SUBMODULES "" or not passing
GIT_SUBMODULE at all is the same, and the behavior is to initialize and update ALL the submodules.