+1 to ignore pre-release mappings.

But an NPE is not acceptable as we just can't rely on the format of the datastore, for example I'd hope we could support also the case of reading/search on data which was written by other tools.

I can see how some people might want to write on ES on their own, and try to forge an "Hibernate Search compliant schema" so to help with that we should be rather lenient in the data expectations.

Also we should be prepared to face situations in which people deploy multiple Hibernate Search powered applications targeting the same ES cluster; these independent applications might need to evolve independently, e.g. not to force them all to use the same Hibernate Search version.