--- 1. single element: discriminator present ---
{"paymentType":"credit_card","amountDue":99.99,"cardNetwork":"VISA","cardNumberLastFour":"4242","paymentId":1}
--- 2. BROKEN: writeValueAsString(List) drops paymentType ---
[{"amountDue":99.99,"cardNetwork":"VISA","cardNumberLastFour":"4242","paymentId":1},{"amountDue":250.0,"bankAccountIban":"GB29NWBK60161331926819","bankName":"National Bank","paymentId":2}]
--- 3. FIX A: writerFor(TypeReference) ---
[ {
  "paymentType" : "credit_card",
  "amountDue" : 99.99,
  "cardNetwork" : "VISA",
  "cardNumberLastFour" : "4242",
  "paymentId" : 1
}, {
  "paymentType" : "bank_transfer",
  "amountDue" : 250.0,
  "bankAccountIban" : "GB29NWBK60161331926819",
  "bankName" : "National Bank",
  "paymentId" : 2
} ]
--- 4. FIX B: a typed array carries its component type ---
[{"paymentType":"credit_card","amountDue":99.99,"cardNetwork":"VISA","cardNumberLastFour":"4242","paymentId":1},{"paymentType":"bank_transfer","amountDue":250.0,"bankAccountIban":"GB29NWBK60161331926819","bankName":"National Bank","paymentId":2}]