Optional Property

GrowthBook/src/commonMain/kotlin/com/sdk/growthbook/evaluators/GBFeatureEvaluator.kt

@@ -11,6 +11,7 @@ import com.sdk.growthbook.model.GBExperimentResult
 import com.sdk.growthbook.model.GBFeature
 import com.sdk.growthbook.model.GBFeatureResult
 import com.sdk.growthbook.model.GBFeatureSource
+import com.sdk.growthbook.utils.OptionalProperty
 import kotlinx.serialization.json.JsonElement
 import kotlinx.serialization.json.jsonObject
 
@@ -161,7 +162,7 @@ internal class GBFeatureEvaluator {
                     /**
                      * Feature value is being forced
                      */
-                    if (rule.force != null) {
+                    if (rule.force is OptionalProperty.Present) {
 
                         /**
                          * If it's a conditional rule, skip if the condition doesn't pass
@@ -240,7 +241,7 @@ internal class GBFeatureEvaluator {
                         }
                         val forcedFeatureResult =
                             prepareResult(
-                                value = rule.force,
+                                value = rule.force.value,
                                 source = GBFeatureSource.force
                             )
 

GrowthBook/src/commonMain/kotlin/com/sdk/growthbook/model/GBFeature.kt

@@ -6,6 +6,8 @@ import com.sdk.growthbook.utils.GBFilter
 import com.sdk.growthbook.utils.GBTrackData
 import com.sdk.growthbook.utils.GBVariationMeta
 import com.sdk.growthbook.utils.GBParentConditionInterface
+import com.sdk.growthbook.utils.OptionalProperty
+import com.sdk.growthbook.utils.OptionalPropertySerializer
 import com.sdk.growthbook.utils.RangeSerializer
 import kotlinx.serialization.Serializable
 import kotlinx.serialization.json.JsonArray
@@ -57,8 +59,8 @@ data class GBFeatureRule(
     /**
      * Immediately force a specific value (ignore every other option besides condition and coverage)
      */
-    val force: JsonElement? = null,
-
+    @Serializable(with = OptionalPropertySerializer::class)
+    val force: OptionalProperty<JsonElement?> = OptionalProperty.NotPresent,
     /**
      * Run an experiment (A/B test) and randomly choose between these variations
      */

GrowthBook/src/commonMain/kotlin/com/sdk/growthbook/utils/Constants.kt

@@ -5,6 +5,7 @@ import com.sdk.growthbook.model.GBFeature
 import com.sdk.growthbook.model.GBFeatureResult
 import kotlinx.serialization.KSerializer
 import kotlinx.serialization.Serializable
+import kotlinx.serialization.SerializationException
 import kotlinx.serialization.builtins.ListSerializer
 import kotlinx.serialization.builtins.PairSerializer
 import kotlinx.serialization.builtins.serializer
@@ -313,3 +314,34 @@ object RangeSerializer {
         }
     }
 }
+
+/**
+ * Wrapper for deserialized model with optional field
+ */
+sealed class OptionalProperty<out T> {
+    object NotPresent : OptionalProperty<Nothing>()
+    data class Present<T>(val value: T) : OptionalProperty<T>()
+}
+
+/**
+ * Serializer for optional properties
+ */
+open class OptionalPropertySerializer<T>(
+    private val valueSerializer: KSerializer<T>
+) : KSerializer<OptionalProperty<T>> {
+    final override val descriptor: SerialDescriptor = valueSerializer.descriptor
+
+    final override fun deserialize(decoder: Decoder): OptionalProperty<T> =
+        OptionalProperty.Present(valueSerializer.deserialize(decoder))
+
+    final override fun serialize(encoder: Encoder, value: OptionalProperty<T>) {
+        when (value) {
+            OptionalProperty.NotPresent -> throw SerializationException(
+                "Tried to serialize an optional property that had no value present." +
+                    " Is encodeDefaults false?"
+            )
+            is OptionalProperty.Present ->
+                valueSerializer.serialize(encoder, value.value)
+        }
+    }
+}