Grape presents has a json nil value

Question

I am presenting an object with a json field with grape.

present my_entry, with: Entities::MyEntity::Create

I am having a weird problem

puts my_entry.content 
{ "test" => "ok" }

present my_entry, with: Entities::MyEntity::Create
{ "test" => nil }
                

In my entity I am exposing the test field

 expose(
   :test,
   documentation: {
     type: String
   }
 )