Add defensive assert for having a weak, empty presistent in a

src/global-handles.cc

Index: src/global-handles.cc
diff --git a/src/global-handles.cc b/src/global-handles.cc
index d6cd47918115799311e4409c9c4500083265aead..82b5f3d96b581674b29c8255b95f1cda1594b23a 100644
--- a/src/global-handles.cc
+++ b/src/global-handles.cc
@@ -207,6 +207,7 @@ class GlobalHandles::Node {
   void MakeWeak(void* parameter, WeakCallback weak_callback) {
     ASSERT(weak_callback != NULL);
     ASSERT(state() != FREE);
+    CHECK(object_ != NULL);
     set_state(WEAK);
     set_parameter(parameter);
     weak_callback_ = weak_callback;