>There is nothing gained from this change. We still have to supply a character to prettify_message and it's the same: default(char) aka \0.

The defaults are supposed to be set in the constructor of the `xxxOptions` type. I'd rather not expose `\0` as an already set property. Beside this, I see `\0` as a libgit2 implementation detail  and I'm sure it would make much sense to expose this at at the LibGit2Sharp API level.