to sneak in docs that don't match the mold/ don't have a unique id (not sure if that's good or not).
Probably not a good idea, but I don't think we should change the functionality with this patch, just the error message. SOLR-139, requires a new add document command - that would be a good place to introduce more rigorous constraints.
I'm pretty sure there are some tests that do this though.
I don't think so. All the tests pass if you throw an exception with a missing ID.
