Omit storageClassName if it is null

Fixes #226

charts/helm-dashboard/templates/pvc.yaml

@@ -14,8 +14,10 @@ spec:
   {{- if .Values.dashboard.persistence.hostPath }}
   storageClassName: ""
   {{- else }}
+  {{- if kindIs "string" .Values.dashboard.persistence.storageClass }}
   storageClassName: "{{ .Values.dashboard.persistence.storageClass }}"
   {{- end }}
+  {{- end }}
   accessModes:
   {{- if not (empty .Values.dashboard.persistence.accessModes) }}
   {{- range .Values.dashboard.persistence.accessModes }}

charts/helm-dashboard/values.yaml

@@ -43,7 +43,7 @@ dashboard:
     ##   set, choosing the default provisioner.  (gp2 on AWS, standard on
     ##   GKE, AWS & OpenStack)
     ##
-    storageClass: ""
+    storageClass: null
 
     ## Helm Dashboard Persistent Volume access modes
     ## Must match those of existing PV or dynamic provisioner