Tweak Kotlin keep rules

retrofit/src/main/resources/META-INF/proguard/retrofit2.pro

@@ -35,10 +35,11 @@
 -if interface * { @retrofit2.http.* <methods>; }
 -keep,allowobfuscation interface * extends <1>
 
-# With R8 full mode generic signatures are stripped for classes that are not
-# kept. Suspend functions are wrapped in continuations where the type argument
-# is used.
+# With R8 full mode generic signatures are stripped for classes that are not kept.
+# Suspend functions are wrapped in continuations where the type argument is used.
 -keep,allowobfuscation,allowshrinking class kotlin.coroutines.Continuation
+# We support Reulst as the return type, need to keep it in R8 full mode.
+-keep,allowobfuscation,allowshrinking class kotlin.Result
 
 # R8 full mode strips generic signatures from return types if not kept.
 -if interface * { @retrofit2.http.* public *** *(...); }