I think requiring a performance test for a change like this is a little excessive. It is blocking, in the same way performing addition of 2 numbers or concatenating a string is blocking, but they're really just memory-only operations.

If we are building a platform that is intended to be extensible by others, this really should be copied / cloned since it is cached in-memory, and the fact that *we* don't modify the object in memory doesn't change the importance of cloning it.

We do use _.extend in quite a few places I think, I figured it sufficed here because the tenant object is only primitive keys, no nested objects.