Helm chart fails with "nil pointer evaluating interface {}" when trying to evaluate a missing nested key

Question

I am writing a Helm 3 library chart and would like to create a YAML with default values. However, when trying to set a default value for a nested key that does not exist, Helm fails with the following error message:

nil pointer evaluating interface {}

Say I have this snippet in my Kubernetes object:

{{- if eq (.Values.deployment.scale.type | default "static") "static" }}
  replicas: {{ default "3" .Values.deployment.scale.replicas }}
{{- end }}

If .Values.deployment.scale is defined, the template will render fine and the value of replicas will be 3 even if .Values.deployment.scale.replicas is not defined.

However, if one of the parent keys is not defined, Helm will fail with the error message above. For example if values.yaml is the following:

# values.yaml
deployment:
  not_scale: {}

The render will fail with: nil pointer evaluating interface {}.scale

How is it possible to set a default value for a nested key, even if its parent keys are undefined?

Answer 1

I've decided to solve this using step-by-step evaluation of the hierarchy and using default dict to assign an empty map if the key does not exist. It both works and looks better.

Example:

{{ $deployment := default dict .Values.deployment }}
{{ $scale      := default dict $deployment.scale }}
{{- if eq ($scale.type | default "static") "static" }}
  replicas: {{ default "3" $scale.replicas }}
{{- end }}