Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/svg/SVGFEMergeElement.cpp

 /*
  * Copyright (C) 2004, 2005, 2007 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006 Rob Buis <buis@kde.org>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 30 matching lines @@
 }
 
 PassRefPtr<FilterEffect> SVGFEMergeElement::build(SVGFilterBuilder* filterBuilder, Filter* filter)
 {
     RefPtr<FilterEffect> effect = FEMerge::create(filter);
     FilterEffectVector& mergeInputs = effect->inputEffects();
     for (Element* element = ElementTraversal::firstWithin(*this); element; element = ElementTraversal::nextSibling(*element)) {
         if (element->hasTagName(SVGNames::feMergeNodeTag)) {
             FilterEffect* mergeEffect = filterBuilder->getEffectById(AtomicString(toSVGFEMergeNodeElement(element)->in1()->currentValue()->value()));
             if (!mergeEffect)
-                return 0;
+                return nullptr;
             mergeInputs.append(mergeEffect);
         }
     }
 
     if (mergeInputs.isEmpty())
-        return 0;
+        return nullptr;
 
     return effect.release();
 }
 
 }