To reproduce:
set system config-management commit-archive location 'tftp://172.16.20.200/CONFIGS/vyos'
vyos@vyos# commit [ nat source rule 9 outbound-interface pppoe0 ] NAT configuration warning: interface pppoe0 does not exist on this system Use of uninitialized value $source_address in concatenation (.) or string at /etc/commit/post-hooks.d/02vyatta-commit-push.pl line 78. Archiving config... tftp://172.16.20.200/CONFIGS/vyos [edit]