Make charts compatible with older Helm versions

[eliobischof]

As a developer, I don't want Helm to throw nil pointers, even when I use an old Helm version.

Acceptance Criteria

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1. The chart is installable with a Helm binary version that is compiled with go v1.17
2. The chart is installable with a Helm binary version that is compiled with go v1.18

Details:
#53 (comment)