The nagios exporter appears to export the value for display_name, even if it's blank.
Since this parameter is optional to nagios, it hasn't been filled out for most hosts on my install.
When I exported this to nagios, hosts.cfg is full of lines looking like this:
which in-turn causes blank display names in the Icinga Web-UI.
Now of course the simple fix is to fill this out, but it would be cleaner if the exporter handled this better.
A simple workaround for now is:
grep -v display_name hosts.cfg > hosts.tmp
mv hosts.tmp hosts.cfg