Remove NULL in xfa/

xfa/fwl/lightwidget/cfwl_checkbox.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_CHECKBOX_H_
 #define XFA_FWL_LIGHTWIDGET_CFWL_CHECKBOX_H_
 
 #include "xfa/fwl/basewidget/ifwl_checkbox.h"
 #include "xfa/fwl/lightwidget/cfwl_widget.h"
 
 class CFWL_CheckBox : public CFWL_Widget {
  public:
   CFWL_CheckBox();
   ~CFWL_CheckBox() override;
 
   static CFWL_CheckBox* Create();
 
-  FWL_Error Initialize(const CFWL_WidgetProperties* pProperties = NULL);
+  FWL_Error Initialize(const CFWL_WidgetProperties* pProperties = nullptr);
   FWL_Error SetCaption(const CFX_WideStringC& wsCaption);
   FWL_Error SetBoxSize(FX_FLOAT fHeight);
   int32_t GetCheckState();
   FWL_Error SetCheckState(int32_t iCheck);
 
  protected:
   class CFWL_CheckBoxDP : public IFWL_CheckBoxDP {
    public:
     CFWL_CheckBoxDP();
 
     // IFWL_DataProvider
     FWL_Error GetCaption(IFWL_Widget* pWidget,
                          CFX_WideString& wsCaption) override;
 
     // IFWL_CheckBoxDP
     FX_FLOAT GetBoxSize(IFWL_Widget* pWidget) override;
 
     FX_FLOAT m_fBoxHeight;
     CFX_WideString m_wsCaption;
   };
 
   CFWL_CheckBoxDP m_checkboxData;
 };
 
 #endif  // XFA_FWL_LIGHTWIDGET_CFWL_CHECKBOX_H_