Unable to read files using common library - kubernetes-helm

Question

I have an issue when trying to use a file from a library chart. Helm fails when I try to access a file from the library.
I have followed the example from the library_charts documentation.
Everything is the same as the documentation except two parts:
I have added the file mylibchart/files/foo.conf and this file is referenced in mylibchart/templates/_configmap.yaml's data key (in the documentation, data is an empty object):
├── mychart
│ ├── Chart.yaml
│ └── templates
│ └── configmap.yaml
└── mylibchart
├── Chart.yaml
├── files
│ └── foo.conf
└── templates
├── _configmap.yaml
└── _util.yaml
cat mylibchart/templates/_configmap.yaml
{{- define "mylibchart.configmap.tpl" -}}
apiVersion: v1
kind: ConfigMap
metadata:
name: {{ .Release.Name | printf "%s-%s" .Chart.Name }}
data:
fromlib: yes
{{ (.Files.Glob "files/foo.conf").AsConfig | nindent 2 }}
{{- end -}}
{{- define "mylibchart.configmap" -}}
{{- include "mylibchart.util.merge" (append . "mylibchart.configmap.tpl") -}}
{{- end -}}
This error is caused by the fact that mychart/files/foo.conf does not exist. If I create it, it does not crash, but contains mychart/files/foo.conf's content instead of mylibchart/files/foo.conf's content.
The file foo.conf does exist inside the file generated by "helm dependency update" (mychart/charts/mylibchart-0.1.0.tgz).
How can I use that file from the .tgz file?
You can easy reproduce the issue by cloning the project: https://github.com/florentvaldelievre/helm-issue
Helm version:
version.BuildInfo{Version:"v3.2.3", GitCommit:"8f832046e258e2cb800894579b1b3b50c2d83492", GitTreeState:"clean", GoVersion:"go1.13.12"}