Going along the readme for the common package, it's suggested many times
to use the templates with no values inside, for example:
```
{{- template "common.ingress" (list . "mychart.ingress") -}}
{{- define "mychart.ingress" -}}
{{- end -}}
```
This will give the following error:
```
Error: rendering template failed: assignment to entry in nil map
```
By adding empty dict defaults, we can fix the code and respect the README
Signed-off-by: Javier Domingo Cansino <javierdo1@gmail.com>