[opentelemetry-kube-stack] Custom collectors missing empty `volumes` and `volumeMounts` arrays during dry-runs

[kitforbes]

When using a custom collector (not a preset) without any volumes or volumeMounts, the chart will render an empty field (null)

apiVersion: opentelemetry.io/v1beta1
kind: OpenTelemetryCollector
metadata:
  name: custom
spec:
  volumeMounts:
  volumes:

This is fine during installation, but when working with something like Flux when driftDetection is enabled, this will throw an error as the spec won't accept null.

cannot determine release state: unable to determine cluster state: OpenTelemetryCollector/monitoring/otel-gateway dry-run failed (Invalid): OpenTelemetryCollector.opentelemetry.io "otel-gateway" is invalid: [spec.volumes: Invalid value: "null": spec.volumes in body must be of type array: "null", spec.volumeMounts: Invalid value: "null": spec.volumeMounts in body must be of type array: "null"]

Ideally the empty arrays would be declared

apiVersion: opentelemetry.io/v1beta1
kind: OpenTelemetryCollector
metadata:
  name: custom
spec:
  volumeMounts: []
  volumes: []

Copying the implementation from your securityContext, this could be implemented in this way:

diff --git a/charts/opentelemetry-kube-stack/templates/collector.yaml b/charts/opentelemetry-kube-stack/templates/collector.yaml
index d99459b5..eb0b579b 100644
--- a/charts/opentelemetry-kube-stack/templates/collector.yaml
+++ b/charts/opentelemetry-kube-stack/templates/collector.yaml
@@ -113,6 +113,7 @@ spec:
   {{- toYaml . | nindent 4}}
   {{- end }}
   volumeMounts:
+  {{- if or $collector.presets.logsCollection.enabled $collector.presets.hostMetrics.enabled $collector.volumeMounts }}
   {{- if $collector.presets.logsCollection.enabled }}
   - name: varlogpods
     mountPath: /var/log/pods
@@ -134,6 +135,9 @@ spec:
   {{- with $collector.volumeMounts }}
   {{- toYaml . | nindent 2 }}
   {{- end }}
+  {{- else }}
+  {{- toYaml $collector.volumeMounts | nindent 4 }}
+  {{- end }}
   {{- with $collector.ports }}
   ports:
   {{- toYaml . | nindent 4 }}
@@ -180,6 +184,7 @@ spec:
   {{- toYaml . | nindent 4 }}
   {{- end }}
   volumes:
+  {{- if or $collector.presets.logsCollection.enabled $collector.presets.hostMetrics.enabled $collector.volumes }}
   {{- if $collector.presets.logsCollection.enabled }}
   - name: varlogpods
     hostPath:
@@ -202,6 +207,9 @@ spec:
   {{- with $collector.volumes }}
   {{- toYaml . | nindent 2 }}
   {{- end }}
+  {{- else }}
+  {{- toYaml $collector.volumes | nindent 4 }}
+  {{- end }}
   {{- with $collector.initContainers }}
   initContainers:
   {{- toYaml . | nindent 4 }}