Get rid of NULLs in core/

core/fdrm/crypto/fx_crypt.cpp

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #include "core/fdrm/crypto/include/fx_crypt.h"
 
 #ifdef __cplusplus
 extern "C" {
@@ skipping 230 matching lines @@
                        uint32_t length,
                        uint8_t digest[16]) {
   md5_context ctx;
   CRYPT_MD5Start(&ctx);
   CRYPT_MD5Update(&ctx, input, length);
   CRYPT_MD5Finish(&ctx, digest);
 }
 static FX_BOOL (*g_PubKeyDecryptor)(const uint8_t* pData,
                                     uint32_t size,
                                     uint8_t* data_buf,
-                                    uint32_t& data_len) = NULL;
+                                    uint32_t& data_len) = nullptr;
 void CRYPT_SetPubKeyDecryptor(FX_BOOL (*func)(const uint8_t* pData,
                                               uint32_t size,
                                               uint8_t* data_buf,
                                               uint32_t& data_len)) {
   g_PubKeyDecryptor = func;
 }
 #ifdef __cplusplus
 };
 #endif