API Gateway: Headers integration lambda parameters was lost on deply

[ZextrasGiacomoMattiuzzi]

I have this yaml configuration for my API Gateway:
/provisioning: methods: - GET responses: - code: "200" parameters: method.response.header.Content-Type: true integration: lambda: src:provisioning responses: - pattern: "" code: "200" parameters: method.response.header.Content-Type: "'application/json'" template: text/plain: | $input.path('$')
But when i go to APIGateway Resource, there are a Content-Type key present under response integration but value is empty..
I try with and w/out single quote wrap on value but without success. I need to set Content-Type and every other header key by hand