check if list contains item in Helm chart

I have a chart that I want to deploy if a certain value is in a list of values. I've tried the following

{{if .Release.Namespace in .Values.Namespaces }}
   <chart goes here>
{{ end }}

where the values file used contains the following

Namespaces:
  -value1
  -value2

but i get an error function "in" not defined

Searching the interwebs I've been unable to find what the proper syntax is for checking if a value exists in a list in helm.