Kotlin/Room Error: Parameter specified as non-null is null: method kotlin.jvm.internal.Intrinsics.checkParameterIsNotNull, parameter messages

Question

Not sure what is causing this, but i am trying request data from the api which includes an array of Message objects. If i print the result to the console, the data is correct apart from Messages=null when i would expect Message to be an array of objects. I can't understand what i've missed?

I'm getting this error: java.lang.IllegalArgumentException: Parameter specified as non-null is null: method kotlin.jvm.internal.Intrinsics.checkParameterIsNotNull, parameter messages

Could anyone point me in the right direction? Code below for the class:

const val PROFILE_RESPONSE_ID = 0

@Entity(tableName = "profile")
data class ProfileResponse(
    val id: Int,
    val name: String,
    val code: String,
    val title: String,
    @SerializedName("profile_image")
    val profileImage: String,
    @SerializedName("background_image")
    val backgroundImage: String,
    @Embedded(prefix = "messages_")
    val messages: ArrayList<Messages>,
) {
    @PrimaryKey(autoGenerate = false)
    var responseId: Int = PROFILE_RESPONSE_ID
}

Sample JSON:

{
  "id": 44,
  "name": "Jason",
  "code": "jason",
  "title": "Jason Scott",
  "profile_image": "https://sampleurl.com/sample_profile.jpg",
  "background_image": "",
  "messages": [
    {
      "id": 0001,
      "message": "Aenean eu leo quam. Pellentesque ornare sem lacinia quam venenatis vestibulum.",
      "timestamp": "Thu, 01 Jan 1970 01:00:00 +0100",
    }
    {
      "id": 0002,
      "message": "Aenean eu leo quam. Pellentesque ornare sem lacinia quam venenatis vestibulum.",
      "timestamp": "Thu, 01 Jan 1970 01:00:00 +0100",
    }
    {
      "id": 0003,
      "message": "Aenean eu leo quam. Pellentesque ornare sem lacinia quam venenatis vestibulum.",
      "timestamp": "Thu, 01 Jan 1970 01:00:00 +0100",
    }
}

Like you mentioned messages is null but the kotlin compiler thinks messages not null and you're trying to set it null. — Srikar Reddy
– Srikar Reddy, Commented Jan 8, 2019 at 17:28
But it shouldn't be null nor am i trying to set it to be null (not intentionally anyway), it should have the array of message objects pulled down from the api? — Jason
– Jason, Commented Jan 8, 2019 at 17:29
Check if the server is sending you the messages_ json object and it is properly getting converted to array list of messages. — Srikar Reddy
– Srikar Reddy, Commented Jan 8, 2019 at 17:34
Not sure if this makes much difference but originally was List<Messages> but was getting e: error: Entities and Pojos must have a usable public constructor. You can have an empty constructor or a constructor whose parameters match the fields (by name and type). - java.util.List so converted it to a List. Does it need to be a List or should ArrayList work just fine? (or an array of objects) — Jason
– Jason, Commented Jan 8, 2019 at 17:39
@Jason Embedded works for a single object to embed its fields in the entity table. In the case of a List of objects, you have a one to many relation and this is modeled in Room with a Relation annotation in a new pojo(along with some changes to your current code). developer.android.com/training/data-storage/room/… — user
– user, Commented Jan 9, 2019 at 10:48

Jason · Accepted Answer · 2019-01-09 12:26:29Z

Managed to solve this by removing @Embedded as I didn't necessarily need the data in another table, and added a TypeConverter to convert the list into a String and back (This question helped). For reference for anyone else:

TypeConvertor Class

class Convertors {

    @TypeConverter
    fun listToJson(value: List<Message>?): String {
        return Gson().toJson(value)
    }

    @TypeConverter
    fun jsonToList(value: String): List<Message>? {
        val objects = Gson().fromJson(value, Array<Message>::class.java) as Array<Message>
        val list = objects.toList()
        return list
    }

}

Then adding the @TypeConverters to my database class.

Database Class

@Database(entities = [ProfileResponse::class], version = 1)
@TypeConverters(Convertors::class)
abstract class MainDatabase: RoomDatabase() {

    abstract fun profileResponseDao(): ProfileResponseDao

}

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