I think your connector documentation (https://developer.couchbase.com/documentation/server/current/connectors/spark-2.1/spark-intro.html) has everything to answer your questions. On connect you can open more buckets like:
.config("spark.couchbase.bucket.beer-sample", "") // open the beer-sample bucket with empty password
.config("spark.couchbase.bucket.foo", "bar") // open the foo bucket with password bar
You can try setting the value of the config as "", this might work as well. Also, we always recommend to set passwords anyways.
Keep in mind that if you open more than one bucket on each op against couchbase you need to specify he bucket name, since the connector doesn't know which one you want. See our docs for each method on how to do that.