Cbimport documentation issue in Couchbase server 6.0

In Couchbase 6.0 :
it says below as optional : Optional

-g,–generate-key <key_expr>

However as per my server version when I see usage of cbimport in command line it say key is mandatory .
Please correct the discrepancies for the benefit of others .
cbimport version 1.0.1 (8b89281) Couchbase server 6.0