Remove NULL in xfa/

xfa/fwl/lightwidget/cfwl_pushbutton.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_FWL_LIGHTWIDGET_CFWL_PUSHBUTTON_H_
 #define XFA_FWL_LIGHTWIDGET_CFWL_PUSHBUTTON_H_
 
 #include "xfa/fwl/basewidget/ifwl_pushbutton.h"
 #include "xfa/fwl/lightwidget/cfwl_widget.h"
 
 class CFWL_PushButton : public CFWL_Widget {
  public:
   CFWL_PushButton();
   ~CFWL_PushButton() override;
 
   static CFWL_PushButton* Create();
 
-  FWL_Error Initialize(const CFWL_WidgetProperties* pProperties = NULL);
+  FWL_Error Initialize(const CFWL_WidgetProperties* pProperties = nullptr);
   FWL_Error GetCaption(CFX_WideString& wsCaption);
   FWL_Error SetCaption(const CFX_WideStringC& wsCaption);
   CFX_DIBitmap* GetPicture();
   FWL_Error SetPicture(CFX_DIBitmap* pBitmap);
 
  protected:
   class CFWL_PushButtonDP : public IFWL_PushButtonDP {
    public:
-    CFWL_PushButtonDP() : m_pBitmap(NULL) {}
+    CFWL_PushButtonDP() : m_pBitmap(nullptr) {}
 
     // IFWL_DataProvider
     FWL_Error GetCaption(IFWL_Widget* pWidget,
                          CFX_WideString& wsCaption) override;
 
     // IFWL_PushButtonDP
     CFX_DIBitmap* GetPicture(IFWL_Widget* pWidget) override;
 
     CFX_WideString m_wsCaption;
     CFX_DIBitmap* m_pBitmap;
   };
 
   CFWL_PushButtonDP m_buttonData;
 };
 
 #endif  // XFA_FWL_LIGHTWIDGET_CFWL_PUSHBUTTON_H_