I need to index a property in a Couchbase Lite database, and the property is optional, i.e. not present in all documents. I wanted to know if this kind of indexing is supported in Couchbase Lite.
Yes.
It is entirely possible to put an index on a property that is not present in all documents or a property whose value is nil in some documents.
Documents with properties like that might be represented in Swift, as Optionals.