The on-not-found="fail|warn|ignore" configuration option controls the behavior when a subject can not be found.

<source-subject-identifiers>
<source-subject-identifier source="jdbc" subject-attribute="id">
<ldap-search base="ou=testpeople,${base}" scope="subtree_scope" filter="(cn=

{0}

)"
on-not-found="warn" />
</source-subject-identifier>
</source-subject-identifiers>

If the subject with cn=X can not be found,

if on-not-found="fail" then an exception will be thrown and the running process will terminate immediately
if on-not-found="warn" then a warning will be logged and the process will continue
if on-not-found="ignore" then the process will continue, nothing will be logged

The default if not specified is "warn".