Now everything at least compiles, though doing nothing
diff --git a/model/sync-state.h b/model/sync-state.h
index c6511e5..84abea6 100644
--- a/model/sync-state.h
+++ b/model/sync-state.h
@@ -41,7 +41,7 @@
 class State
 {
 public:
-  virtual ~State () = 0;
+  virtual ~State () { };
   
   /**
    * @brief Add or update leaf to the state tree