startup error after converting to slapd-config

Dear all,

We run openLDAP 2.4.21 on one master plus 7 slaves. Some time ago ( I believe we were on 2.4.19 at 
the time ), I converted one of the slaves to slapd-config from slapd.conf to get myself acquainted 
with it, and that went without problems. Now, if I try the conversion with slaptest -f slapd.conf -F 
slapd.d, the conversion works ok, but slapd won't start, and gives this error:

Jan 18 15:30:20 7E:example-slave slapd[1741992]: _sasl_plugin_load failed on sasl_auxprop_plug_init 
for plugin: ldapdb
Jan 18 15:30:20 7U:example-slave slapd[1741992]: olcSyncrepl: value #0: <olcSyncrepl> invalid URL
Jan 18 15:30:20 7U:example-slave slapd[1741992]: config error processing 
olcDatabase={1}hdb,cn=config: <olcSyncrepl> invalid URL
Jan 18 15:30:20 7U:example-slave slapd[1741992]: slapd stopped.
Jan 18 15:30:20 7U:example-slave slapd[1741992]: connections_destroy: nothing to destroy.

I noticed that the olcSyncrepl in olcDatabase={1}hdb,cn=config changed from:

olcSyncrepl: rid=001 provider=ldap://masterldap.example.com:389 bindmethod=simple timeout
  =0 network-timeout=0 binddn="cn=syncuser,dc=example,dc=com" credentials="xxxxxxxxx
  " starttls=critical filter="(objectClass=*)" searchbase="dc=example,dc=com" scope=
  sub attrs="*,+" schemachecking=off type=refreshAndPersist retry="5 5 10 +"

for the older openldap version, to:

olcSyncrepl: rid=001 provider=ldap://masterldap.example.com:389 uri="" bindmethod=simple
  timeout=0 network-timeout=0 binddn="cn=syncuser,dc=example,dc=com" credentials="xxxxxxxxx" 
starttls=critical tls_cert="/usr/ssl/certs/examplewildcard.cert
  " tls_key="/usr/ssl/certs/examplewildcard.key" tls_cacert="/usr
  /ssl/certs/cacert_root.crt" tls_reqcert=demand tls_crlcheck=none filter="(obj
  ectClass=*)" searchbase="dc=example,dc=com" scope=sub attrs="*,+" schemachecking=o
  ff type=refreshAndPersist retry="5 5 10 +"

for 2.4.21.
Notice the ' uri="" ' in the last version.

Fortunately, if I remove the empty uri assignment from the ldif file, slapd starts normally. But I 
still wondered if I have missed something, so if anyone can explain what happened, I would be very 
grateful.
Best regards,

gerard