How to fix Helm "installation failed" complaning about a nil pointer evaluating interface on fullnameOverride

I am building a new Helm chart (mychart) that I'm trying to install.

A values.yaml exists and its contents specify the fullnameOverride:

fullnameOverride: "myapp"

I run the following command

helm install --dry-run -f "mychart-stack/values.yaml" mychart-stack1 ./mychart-stack

And it's giving me the error:
> template: mychart-stack/templates/persistentvolume.local-storage.range.yml:5:14: executing "mychart-stack/templates/persistentvolume.local-storage.range.yml" at <include "mychart-stack.fullname" .>: error calling include: template: mychart-stack/templates/_helpers.tpl:14:14: executing "mychart-stack.fullname" at <.Values.fullnameOverride>: nil pointer evaluating interface {}.fullnameOverride

The mychart-stack/templates/_helpers.tpl:14:14 is the pregenerated one when you're asking Helm to produce a Chart example.

The error (14:14) is associated at the first line of the following auto generated code:

{{- if .Values.fullnameOverride }}
{{- .Values.fullnameOverride | trunc 63 | trimSuffix "-" }}
{{- else }}

A little more context, as it's throwing an error while checking the persistentvolume.local-storage.range.yml, here are the contents of the file:

{{- range .Values.persistentVolume.localStorage }}
---
apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-{{ include "mychart-stack.fullname" }}-{{ .name }}
spec:
  capacity:
    storage: 20Gi
  # le champ volumeMode requiert l'activation de la "feature gate" Alpha BlockVolume
  volumeMode: Filesystem
  accessModes:
  - ReadWriteOnce
  persistentVolumeReclaimPolicy: Retain
  storageClassName: local-storage-{{ include "mychart-stack.fullname" }}--{{ .name }}
  local:
    path: {{ .Values.persistentVolume.basePath }}/{{ .name }}
  nodeAffinity:
    required:
      nodeSelectorTerms:
      - matchExpressions:
        - key: kubernetes.io/hostname
          operator: In
          values:
          - {{ .Values.hostName }}
{{- end }}

I don't know what's wrong, the code seems to indicate that it's not defined properly.
I tried to run it in --debug mode but it doesn't help (same error).

Finally the problem wasn't the values.yaml that was not set correctly but more the way it was used within the template.

When using an include of a definition coming from a .tpl file (this one was the autogenerated by Helm), we must be careful to not be in a range.

I was creating a range of assets so it seems that it will run the code in the context of the range.

> Your conditional logic is being evaluated inside a range loop. This means . you're using to access Values is not the one you expect it to be, as it's overridden for each range iteration evaluation.

ref: https://stackoverflow.com/questions/57475521/ingress-yaml-template-returns-error-in-renderring-nil-pointer-evaluating-int

That means that we should use $ instead of . notation because it references the global scope.

Example:

{{- include "mychart-stack.fullname" $ }}