Remove NULL in xfa/

xfa/fxfa/parser/xfa_document_serialize.h

 // 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
 
 #ifndef XFA_FXFA_PARSER_XFA_DOCUMENT_SERIALIZE_H_
 #define XFA_FXFA_PARSER_XFA_DOCUMENT_SERIALIZE_H_
 
 #include "core/fxcrt/include/fx_string.h"
@@ skipping 15 matching lines @@
 };
 
 class CXFA_DataExporter {
  public:
   explicit CXFA_DataExporter(CXFA_Document* pDocument);
 
   FX_BOOL Export(IFX_FileWrite* pWrite);
   FX_BOOL Export(IFX_FileWrite* pWrite,
                  CXFA_Node* pNode,
                  uint32_t dwFlag = 0,
-                 const FX_CHAR* pChecksum = NULL);
+                 const FX_CHAR* pChecksum = nullptr);
 
  protected:
   FX_BOOL Export(IFX_Stream* pStream,
                  CXFA_Node* pNode,
                  uint32_t dwFlag,
                  const FX_CHAR* pChecksum);
 
   CXFA_Document* const m_pDocument;
 };
 
 #endif  // XFA_FXFA_PARSER_XFA_DOCUMENT_SERIALIZE_H_