refptr allows NULL to be assigned to it

src/common/refptr.h

@@ -84,8 +84,11 @@ template <typename T> void refptr<T>::destroy()
     if (m_refCount != NULL)
     {
         if (*m_refCount <= 1)
+        {
+            if (m_ptr != NULL)
             {
                 delete m_ptr;
+            }
             delete m_refCount;
         }
         else