Don't throw exception if related object can't be found

If a document has a reference to another domain class and the document for that domain class cannot found, it should return null instead of throwing an exception. Add as a configuration option to prevent breaking existing behavior

Start by locating how Grails resolves a referenced domain class and where it raises an exception when the referenced document is missing. Then trace the configuration options for that behavior; done means a configurable option returns null for a missing related document while preserving the existing behavior by default.

Written by the indexing model from the issue text.