Whenever a submodule configuration is parsed in `parse_submodule_config_option`
via e.g. `gitmodules_config()`, it will overwrite the null_sha1 entry.
-So in the normal case, when HEAD:.gitmodules is parsed first and then overlayed
+So in the normal case, when HEAD:.gitmodules is parsed first and then overlaid
with the repository configuration, the null_sha1 entry contains the local
configuration of a submodule (e.g. consolidated values from local git
configuration and the .gitmodules file in the worktree).