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  1. Java Driver
  2. JAVA-5342

Can't encode classes with nullable type parameters

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    • Type: Icon: Bug Bug
    • Resolution: Unresolved
    • Priority: Icon: Unknown Unknown
    • None
    • Affects Version/s: 4.11.1, 5.0.0
    • Component/s: Kotlin
    • Java Drivers
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      1. What would you like to communicate to the user about this feature?
      2. Would you like the user to see examples of the syntax and/or executable code and its output?
      3. Which versions of the driver/connector does this apply to?

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      1. What would you like to communicate to the user about this feature? 2. Would you like the user to see examples of the syntax and/or executable code and its output? 3. Which versions of the driver/connector does this apply to?

      Summary

      Encoding an object that contains a property that has a nullable generic parameter type, like Container in the example below will fail with 

      org.bson.BsonInvalidOperationException: writeString can only be called when State is VALUE, not when State is NAME

      or 

      org.bson.BsonInvalidOperationException: writeNull can only be called when State is VALUE, not when State is NAME

      depending on whether the actual value is null.

      How to Reproduce

      @Serializable
data class Box<T>(
    val boxed: T
)

@Serializable
data class Container(
    // Using a nullable generic causes the exception, Box<String> works fine
    val box: Box<String?>
)

fun main() {
    KotlinSerializerCodec.create<Container>()!!.encode(
        JsonWriter(StringWriter()),
        Container(Box("foo")),
        EncoderContext.builder().build()
    )
}

      run this results in 

      Exception in thread "main" org.bson.BsonInvalidOperationException: writeString can only be called when State is VALUE, not when State is NAME     
 at org.bson.AbstractBsonWriter.throwInvalidState(AbstractBsonWriter.java:747)     
 at org.bson.AbstractBsonWriter.checkPreconditions(AbstractBsonWriter.java:702)     
 at org.bson.AbstractBsonWriter.writeString(AbstractBsonWriter.java:607)     
 at org.bson.codecs.kotlinx.DefaultBsonEncoder.encodeString(BsonEncoder.kt:166)     
 at kotlinx.serialization.internal.StringSerializer.serialize(Primitives.kt:159)     
 at kotlinx.serialization.internal.StringSerializer.serialize(Primitives.kt:156)     
 at kotlinx.serialization.encoding.Encoder$DefaultImpls.encodeSerializableValue(Encoding.kt:279)     
 at kotlinx.serialization.encoding.AbstractEncoder.encodeSerializableValue(AbstractEncoder.kt:18)     
 at kotlinx.serialization.internal.NullableSerializer.serialize(NullableSerializer.kt:23)     
 at kotlinx.serialization.encoding.Encoder$DefaultImpls.encodeSerializableValue(Encoding.kt:279)     
 at kotlinx.serialization.encoding.AbstractEncoder.encodeSerializableValue(AbstractEncoder.kt:18)    
 at kotlinx.serialization.encoding.AbstractEncoder.encodeSerializableElement(AbstractEncoder.kt:80)     
 at org.example.Box.write$Self$a(Test.kt:14)

      Notice that 

      org.example.Box.write$Self$a calls encodeSerializableElement instead of 
      encodeNullableSerializableElement, which might indicate a bug in the kotlinx serialization compiler plugin.
       
      I've already created a fix for this: https://github.com/mongodb/mongo-java-driver/pull/1317
       

            Assignee:
            Unassigned Unassigned
            Reporter:
            cliffred.vanvelzen@edsn.nl Cliffred van Velzen
            Votes:
            1 Vote for this issue
            Watchers:
            4 Start watching this issue

              Created:
              Updated: