GET http://localhost:3000/customers

###
GET http://localhost:3000/customers/-3

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POST http://localhost:3000/customers
Content-Type: application/json

{
  "name": "Max",
  "balance": 1000
}

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PATCH http://localhost:3000/customers/-1
Content-Type: application/json

{
  "name": "Annalisa",
  "balance": 2000
}

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DELETE http://localhost:3000/customers/-2