diff --git a/evaluation-core/src/commonMain/kotlin/EvaluationEngine.kt b/evaluation-core/src/commonMain/kotlin/EvaluationEngine.kt
index 911538e..5df7f0a 100644
--- a/evaluation-core/src/commonMain/kotlin/EvaluationEngine.kt
+++ b/evaluation-core/src/commonMain/kotlin/EvaluationEngine.kt
@@ -16,7 +16,7 @@ interface EvaluationEngine {
     ): Map<String, EvaluationVariant>
 }
 
-class EvaluationEngineImpl(private val log: Logger? = null) : EvaluationEngine {
+class EvaluationEngineImpl(private val log: Logger? = DefaultLogger()) : EvaluationEngine {
 
     data class EvaluationTarget(
         val context: EvaluationContext,
diff --git a/evaluation-core/src/commonMain/kotlin/EvaluationVariant.kt b/evaluation-core/src/commonMain/kotlin/EvaluationVariant.kt
index 44accf5..87239af 100644
--- a/evaluation-core/src/commonMain/kotlin/EvaluationVariant.kt
+++ b/evaluation-core/src/commonMain/kotlin/EvaluationVariant.kt
@@ -8,8 +8,9 @@ import kotlinx.serialization.UseSerializers
 @Serializable
 data class EvaluationVariant(
     val key: String,
-    val value: Any?,
-    val metadata: Map<String, Any?>?,
+    val value: Any? = null,
+    val payload: Map<String, Any?>? = null,
+    val metadata: Map<String, Any?>? = null,
 ) : Selectable {
     override fun select(selector: String): Any? {
         return when (selector) {