Get rid of NULLs in xfa/

xfa/fwl/lightwidget/cfwl_pushbutton.h

Index: xfa/fwl/lightwidget/cfwl_pushbutton.h
diff --git a/xfa/fwl/lightwidget/cfwl_pushbutton.h b/xfa/fwl/lightwidget/cfwl_pushbutton.h
index 5ca3dded3767bcb491c33ac091246b3ccd057eae..fa5b12ebab01dda44f632e3d584cdb350f645837 100644
--- a/xfa/fwl/lightwidget/cfwl_pushbutton.h
+++ b/xfa/fwl/lightwidget/cfwl_pushbutton.h
@@ -13,7 +13,7 @@
 class CFWL_PushButton : public CFWL_Widget {
  public:
   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();
@@ -24,7 +24,7 @@ class CFWL_PushButton : public CFWL_Widget {
  protected:
   class CFWL_PushButtonDP : public IFWL_PushButtonDP {
    public:
-    CFWL_PushButtonDP() : m_pBitmap(NULL) {}
+    CFWL_PushButtonDP() : m_pBitmap(nullptr) {}
     FWL_Error GetCaption(IFWL_Widget* pWidget, CFX_WideString& wsCaption);
     virtual CFX_DIBitmap* GetPicture(IFWL_Widget* pWidget);
     CFX_WideString m_wsCaption;