JSON encoding for Ecto schemas under the API's null policy: string fields encode as "" when nil and map fields as %{} — game clients (Godot in particular) choke on null where they expect a string. Datetimes, numbers and booleans keep null, where absence is semantic.

Used from a hand-written Jason.Encoder impl instead of @derive:

defimpl Jason.Encoder, for: MySchema do
  def encode(struct, opts) do
    Gamend.SchemaJSON.encode(struct, [:id, :title, :icon_url], opts)
  end
end