Convert NULL to nullptr

util/mac/mach_o_image_symbol_table_reader.cc

 // Copyright 2014 The Crashpad Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 248 matching lines @@
   return true;
 }
 
 const MachOImageSymbolTableReader::SymbolInformation*
 MachOImageSymbolTableReader::LookUpExternalDefinedSymbol(
     const std::string& name) const {
   INITIALIZATION_STATE_DCHECK_VALID(initialized_);
 
   const auto& iterator = external_defined_symbols_.find(name);
   if (iterator == external_defined_symbols_.end()) {
-    return NULL;
+    return nullptr;
   }
   return &iterator->second;
 }
 
 }  // namespace crashpad