from Git pull request by rarog:
This is the case for example if the vcard isn't set or has only empty data inside.
Btw this seems to be a regression in 2.7 development branch, the old bug report is here: https://igniterealtime.org/issues/browse/SPARK-820
pull request: https://github.com/igniterealtime/Spark/pull/10
The scenario is quite simple.
Running current nightly Spark 2.7.0 together with an ejabberd server without any LDAP integration.
If a user has an empty vcard then spark shows an empty username (no name or nickname in vCard). This is annoying and when multiple people without any visible nickname. In that case Spark 2.6.3 would show the JID as a fallback. My patch restores this behaviour and prevents blank entries.