Fixed release build issues.

androidApp/proguard-rules.pro

@@ -55,11 +55,38 @@
   public *;
 }
 
--dontwarn com.anupcowkur.reservoir.**
-
 -dontwarn javax.annotation.**
 
 -keep class android.support.v7.widget.SearchView { *; }
 
 # maybe remove later ?
 -keep class * extends androidx.fragment.app.Fragment
+
+
+# Keep `Companion` object fields of serializable classes.
+# This avoids serializer lookup through `getDeclaredClasses` as done for named companion objects.
+-if @kotlinx.serialization.Serializable class **
+-keepclassmembers class <1> {
+   static <1>$Companion Companion;
+}
+
+# Keep `serializer()` on companion objects (both default and named) of serializable classes.
+-if @kotlinx.serialization.Serializable class ** {
+   static **$* *;
+}
+-keepclassmembers class <2>$<3> {
+   kotlinx.serialization.KSerializer serializer(...);
+}
+
+# Keep `INSTANCE.serializer()` of serializable objects.
+-if @kotlinx.serialization.Serializable class ** {
+   public static ** INSTANCE;
+}
+-keepclassmembers class <1> {
+   public static <1> INSTANCE;
+   kotlinx.serialization.KSerializer serializer(...);
+}
+
+# @Serializable and @Polymorphic are used at runtime for polymorphic serialization.
+-keepattributes RuntimeVisibleAnnotations,AnnotationDefault
+