Empty json and Serializable class with no properties or only @EncodedDefault properties

[JavierSegoviaCordoba]

Describe the bug

I am getting a server response which is an empty json { }, I am setting a Serializable class with no properties but I get this exception:

To Reproduce

Set an empty json ({}) and a @Serializable class SomeClass with no properties.

Exception in thread "main" kotlinx.serialization.json.internal.JsonDecodingException: Unexpected JSON token at offset 0: Expected start of the object '{', but had '{' instead
JSON input: {}

Expected behavior

If I get an empty json and I set a @Serializable class with no properties, I expect it to directly work (use case strong typing some error responses by the backend).

If I set a data class which contains one or more @EncodedDefault properties, they should be set.

Environment

• Kotlin version: 1.6.10
• Library version: 1.3.2
• Kotlin platforms: KMP with JVM
• Gradle version: 7.3.3

[ArcticLampyrid]

There is no @EncodedDefault but @EncodeDefault.
And @EncodeDefault is not for marking a property to be optional. What you mean may be a property with default value.

@Target(allowedTargets = [AnnotationTarget.PROPERTY])
annotation class EncodeDefault(mode: EncodeDefault.Mode)

Controls whether the target property is serialized when its value is equal to a default value, regardless of the format settings. Does not affect decoding and deserialization process.

[sandwwraith]

I executed the following test:

    @Serializable class SomeClass

    @Test
    fun testEmpty() {
        val input = "{}"
        println(Json.decodeFromString<SomeClass>(input))
        println(default.decodeFromString<SomeClass>(input))
        println(lenient.decodeFromString<SomeClass>(input))
    }

and it works just fine.

Maybe it has something to do with the encoding of server's response. For example, it may be incorrectly inserted BOM in UTF-8: #1168

[JavierSegoviaCordoba]

Yeah, looks like Ktor issue, I will move to it