[Fix #1865] Expose attachment field over API

app/serializers/champ_serializer.rb

@@ -1,5 +1,15 @@
 class ChampSerializer < ActiveModel::Serializer
+  include Rails.application.routes.url_helpers
+
   attributes :value
 
   has_one :type_de_champ
+
+  def value
+    if object.piece_justificative_file.attached?
+      url_for(object.piece_justificative_file)
+    else
+      object.value
+    end
+  end
 end