It would be nice for a future version of bitcoincore to include a text versions of the error codes so that users can interpret things like -8 means "missing path argument" or something like that without having to post here or grep through source code for the interpretations. Don't get me wrong, error codes are useful and awesome, but eventually it's nice to provide a text based version of the error code along with the numerical one. Really, the numerical one is more useful for API usage.
Open an issue on github.
I will do that, I'm glad you suggested it---I wouldn't have thought to do so otherwise.
