Craft GraphQL APIs in Elixir with Absinthe: trigger uses incorrect arity (page 118)

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Page 118 contains the following trigger code:

trigger :ready_order, topic:
  fn %{ ready: order}, _ -> [order.id]
  _, _ -> []
end

The trigger function in the latest version of absinthe is 1-arity, using 2-arity will cause it to blow up with a cryptic error. The correct code is:

trigger :ready_order, topic:
  fn %{ ready: order} -> [order.id]
  _ -> []
end