Conditionally send variable values

We only want to send trigger variable values if the user is a
maintainer.

app/serializers/trigger_variable_entity.rb

@@ -3,5 +3,6 @@
 class TriggerVariableEntity < Grape::Entity
   include RequestAwareEntity
 
-  expose :key, :value, :public
+  expose :key, :public
+  expose :value, if: ->(_, _) { request.project.team.maintainer?(request.current_user) }
 end