널 가능, 기본값 및 선택적 필드

Real responses skip fields or send null. Your shared models must handle missing data without crashing either app.

Mark a property as nullable with a trailing question mark, and the serializer happily reads a JSON null into it.

A key set to null and a key that is simply absent are different cases, and the library treats each one distinctly.

A property with a default can be left out of the JSON entirely, and decoding fills in your fallback.

In kotlinx.serialization, an optional field just means one that has a default, so absence is never an error.

A non-null property with no default is required. If the JSON omits it, decoding throws a clear exception.

You can combine both: a nullable property that defaults to null tolerates a missing key and a null value alike.

Set explicitNulls to false and the encoder omits null fields instead of writing them out as null.

APIs add fields over time. Turn on ignoreUnknownKeys so new JSON keys never break your existing models.

With coerceInputValues, a null sent for a field that has a default falls back to that default instead of failing.

Combining nullable types, defaults and lenient config makes your shared parsing robust against messy real-world JSON.

How do you let a JSON key be safely omitted from a response?

Use nullable types and defaults for missing data, and tune Json with ignoreUnknownKeys, explicitNulls and coerceInputValues for resilient parsing.