Why does NFS server returns error -22 on nfs4_name_to_uid call?

Issue

• NFS server reports following error in /var/log/messages

May 19 21:54:31 nfsserver rpc.idmapd[29080]: nss_getpwnam: name '500' does not map into domain 'domain-name'
May 19 22:30:48 nfsserver rpc.idmapd[29080]: nss_getpwnam: name '500' does not map into domain 'domain-name'

• Increasing the idmap verbosity, provides the following error logs

May 21 21:14:10 nfsserver rpc.idmapd[26841]: nfsdcb: authbuf=192.168.0.4 authtype=user
May 21 21:14:10 nfsserver rpc.idmapd[26841]: nfs4_name_to_uid: calling nsswitch->name_to_uid
May 21 21:14:10 nfsserver rpc.idmapd[26841]: nss_getpwnam: name '500' domain 'domain-name': resulting localname '(null)'
May 21 21:14:10 nfsserver rpc.idmapd[26841]: nss_getpwnam: name '500' does not map into domain 'domain-name'
May 21 21:14:10 nfsserver rpc.idmapd[26841]: nfs4_name_to_uid: nsswitch->name_to_uid returned -22
May 21 21:14:10 nfsserver rpc.idmapd[26841]: nfs4_name_to_uid: final return value is -22
May 21 21:14:10 nfsserver rpc.idmapd[26841]: Server : (user) name "500" -> id "500"

One way to increase verbosity is to run the rpc.imapd command from the command line, and add one or more '-v' options. See:

# man rpc.imapd

for more details. The additional information will be logged into /var/log/messages.