Proguard obfuscation and generic methods

I'm trying to obfuscate an Android App with ProGuard.

Here I have a class

public class Book implements DBbinded

And a generic method

private void storeDBObjects(ArrayList<? extends DBbinded> dbObjects)

The call of this method throws an java.lang.ClassCastException: java.util.LinkedHashMap after obfuscation. What should I write into proguard.properties to fix this?