Convert NULL to nullptr

util/mac/mac_util.cc

Index: util/mac/mac_util.cc
diff --git a/util/mac/mac_util.cc b/util/mac/mac_util.cc
index da6930c7ec210059e2f7184b76617ddb40f7b168..a792e51197464a30574e4dbea5d79fc91b0fbc24 100644
--- a/util/mac/mac_util.cc
+++ b/util/mac/mac_util.cc
@@ -99,14 +99,14 @@ CFDictionaryRef TryCFCopySystemVersionDictionary() {
   if (_CFCopySystemVersionDictionary) {
     return _CFCopySystemVersionDictionary();
   }
-  return NULL;
+  return nullptr;
 }
 
 CFDictionaryRef TryCFCopyServerVersionDictionary() {
   if (_CFCopyServerVersionDictionary) {
     return _CFCopyServerVersionDictionary();
   }
-  return NULL;
+  return nullptr;
 }
 
 const void* TryCFDictionaryGetValue(CFDictionaryRef dictionary,
@@ -114,7 +114,7 @@ const void* TryCFDictionaryGetValue(CFDictionaryRef dictionary,
   if (value) {
     return CFDictionaryGetValue(dictionary, value);
   }
-  return NULL;
+  return nullptr;
 }
 
 // Converts |version| to a triplet of version numbers on behalf of