Test couchbase v3 client exists command doesn't work

[semistone]

When I test
bucket.defaultCollection().exists(id);
in couchbase v3 API,
It will return UNKNOWN command error

GetMetaRequest failed with unexpected status code UNKNOWN
com.couchbase.client.core.error.CouchbaseException: GetMetaRequest failed with unexpected status code UNKNOWN {"completed":true,"coreId":"0x79feb7be00000001","idempotent":true,"lastChannelId":"79FEB7BE00000001/000000003CB70CF2","lastDispatchedFrom":"127.0.0.1:55345","lastDispatchedTo":"localhost:55340","requestId":10,"requestType":"GetMetaRequest","retried":0,"service":{"bucket":"inventory","collection":"_default","documentId":"test","opaque":"0x12","scope":"_default","type":"kv"},"status":"UNKNOWN","timeoutMs":2500,"timings":{"dispatchMicros":1965,"totalMicros":9548,"serverMicros":0}}

and I compare with client v2, it used the OBSERVE command before
but in v3, it uses the EXISTS command

Is it possible to provide a client v3 example also?

Thanks