security: using new security interfaces of ndn-cpp, such as SecPolicy

Change-Id: Id22c8e711bee7c3723076eda7a3f96c72ca7707c
diff --git a/src/contact-storage.cpp b/src/contact-storage.cpp
index 7ea965c..384e74e 100644
--- a/src/contact-storage.cpp
+++ b/src/contact-storage.cpp
@@ -9,7 +9,6 @@
  */
 
 #include "contact-storage.h"
-#include "null-ptrs.h"
 
 #include <boost/filesystem.hpp>
 #include "logging.h"
@@ -518,7 +517,7 @@
 
       return contact;      
     } 
-  return CHRONOCHAT_NULL_CONTACTITEM_PTR;
+  return shared_ptr<ContactItem>();
 }
 
 shared_ptr<Profile>