const val realmSchemaVersion = 3L // it was 2L

private val config = RealmConfiguration
  .Builder(setOf(MessageRealmObject::class, PendingMessageRealmObject::class))
  .schemaVersion(realmSchemaVersion)
  .build()

@Keep
private class MessageRealmObject : RealmObject {
    @PrimaryKey
    var _id: String? = null
    var chatId: String? = null
    var role: String? = null
    var text: String? = null
    var createdAt: Long? = null
    var photoId: String? = null // new property
    var photoImageUrl: String? = null // new property
}

@Keep
private class PendingMessageRealmObject : RealmObject {
    @PrimaryKey
    var _id: RealmUUID = RealmUUID.random()
    var chatId: String? = null
    var text: String? = null
    var createdAt: Long? = null
}

private fun <T> withRealm(func: (realm: Realm) -> T): T {
    val realm: Realm = Realm.open(config)
    val returnValue = func(realm)
    realm.close()
    return returnValue
}

fun example() {
   // it crashes when withRealm is called.
   withRealm {}
}

java.lang.IllegalStateException: [RLM_ERR_SCHEMA_MISMATCH]: Migration is required due to the following errors:
  - Property 'MessageRealmObject.photoId' has been added.
  - Property 'MessageRealmObject.photoImageUrl' has been added.