A NamespaceStringOrUUID object should only ever hold either a NamespaceString object or a DatabaseName + UUID. Previously, this was enforced because the constructors would only take one or the other, and there were no setters. However, a method NamespaceStringOrUUID::setNss() was added in order to override the namespace for find commands, making it possible to set both the nss and uuid/db name fields. This looks to be used in two places in the find command path - one of these places sets the nss field when the uuid field is already set. There are a number of places that the server relies on the fact that only one of the uuid or nss is set on a NamespaceStringOrUUID object.

I think we should either:

• Remove NamespaceStringOrUUID::setNss() and reconstruct a NamespaceStringOrUUID object instead
• Change NamespaceStringOrUUID::setNss() to also unset the uuid/db name