Some index key generation methods may throw exceptions as part of the control flow, to indicate that a given document has contents which are not compatible with the current set of indexes for a given collection. Collection validation generates the expected keys for each document in order to check them against the index keys on disk for consistency. If an exception is encountered during this process, it fails the validation process early, which could mask other issues.

It is likely we can safely catch certain types of exceptions, record the failure, and continue to validate the rest of the collection. If not, we should make quite clear that the results are incomplete.