SetWithMeta allows key-less docs to be created by clients

Build

4.0.0-2213

In a particular upgrade scenario, the number of docs on a cluster was more than the docs loaded. While analyzing the couch files, I found key less, value-less docs (see screenshot) -

From a single-node cluster:
Arunas-MacBook-Pro:bin apiravi$ ./couch_dbdump ~/Downloads/opt/couchbase/var/lib/couchbase/data/sasl_bucket_1/couch. |grep -v "id: load"|grep -A 7 -B 1 "id"
Doc seq: 6
id:
rev: 1
content_meta: 131
size (on disk): 36
cas: 1432366575452880896, expiry: 0, flags: 0, datatype: 0, conflict_resolution_mode: 0
size: 512
data: (snappy)
Dumping "/Users/apiravi/Downloads/opt/couchbase/var/lib/couchbase/data/sasl_bucket_1/193.couch.1":
–
--
Doc seq: 5
id:
rev: 1
content_meta: 131
size (on disk): 36
cas: 1432366574410727424, expiry: 0, flags: 0, datatype: 0, conflict_resolution_mode: 0
size: 512
data: (snappy)
Dumping "/Users/apiravi/Downloads/opt/couchbase/var/lib/couchbase/data/sasl_bucket_1/657.couch.1":

Attaching logs from .19.

While we have a bug created to handle this inside xdcr, can ep-engine not allow key-less docs to be created?