replace c++11 nullptr with NULL

Debug/DebFile.cc

@@ -135,7 +135,7 @@ public:
 
   void print(const char* const _s, const bool _cnsl = true)
   {
-    if (_s == nullptr)
+    if (_s == NULL)
       return;
     for (int i = 0, c = _s[0]; c != '\0'; c = _s[++i])
       print((char)c, _cnsl);