After booting a router with the nightly build from 31-12-2016 the IfAlias field is empty when doing an snmpwalk.
It seems this is caused by warning messages from Perl on the file /opt/vyatta/sbin/if-mib-alias

The quick fix is to disable these warnings
In the file i added:
no warnings 'experimental::smartmatch';

Just after line 25:
use feature "switch";