"<no value>" after templating

[Z9n2JktHlZDmlhSvqc9X2MmL3BwQG7tk]

Is your feature request related to a problem? Please describe

When I use label name that does not exist in the expression result I get <no value> label value in alert.

Test alerting rule

groups:
  - name: test
    rules:
      - alert: qqq
        expr: 1
        labels:
          alert: problem_only
          host: '{{ $labels.host }}'
#          host_display: '{{ if ne $labels.host "" }}{{ $labels.host }}{{ else }}label host is empty{{ end }}'
          host_display: '{{ if and (ne $labels.host "") (ne $labels.host nil) }}{{ $labels.host }}{{ else }}label host is empty{{ end }}'
        annotations:
          problem: 'just a test'

Prometheus was converting nil to an empty string, so I could use if ne $labels.host "", but now I need to add an extra nil check to all affected alerting rules. It is not so convenient. And what's more, it's not so obvious to check label value against nil (first I tried to check if ne $labels.host "<no value>").

Describe the solution you'd like

Propose to convert non-existent label values to an empty string.
What do you think ?

Describe alternatives you've considered

No response

Additional information

Version: victoria-metrics-20221126-045002-tags-v1.84.0-0-gad105147d
Type: single node

[zekker6]

@hagen1778 What do you think about this?
Maybe adding something like empty filter might make it easier to check values for similar cases?

[zekker6]

@Z9n2JktHlZDmlhSvqc9X2MmL3BwQG7tk Starting from 4a49577 vmalert should convert nil to an empty string similar to Prometheus.
This commit will be a part of the next release.

In the meantime, could you please try the following image and check if it helps?

docker.io/victoriametrics/vmalert:heads-oss-master-0-g4a4957702

If you don't use docker for deployment you can build a binary by using this doc and check if that works for you.

[Z9n2JktHlZDmlhSvqc9X2MmL3BwQG7tk]

Thanks ! I will wait for the next release.

[valyala]

FYI, the issues should be fixed in vmalert v1.90.0.