Take advantage of implicit std::unique_ptr<>(nulltpr_t) ctor.

core/fpdfapi/render/fpdf_render_pattern.cpp

 // 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
 
 #include "core/fpdfapi/render/render_int.h"
 
 #include <algorithm>
 
@@ skipping 801 matching lines @@
     CPDF_Document* pDoc,
     CPDF_PageRenderCache* pCache,
     CPDF_TilingPattern* pPattern,
     const CFX_Matrix* pObject2Device,
     int width,
     int height,
     int flags) {
   std::unique_ptr<CFX_DIBitmap> pBitmap(new CFX_DIBitmap);
   if (!pBitmap->Create(width, height,
                        pPattern->colored() ? FXDIB_Argb : FXDIB_8bppMask)) {
-    return std::unique_ptr<CFX_DIBitmap>();
+    return nullptr;
   }
   CFX_FxgeDevice bitmap_device;
   bitmap_device.Attach(pBitmap.get(), false, nullptr, false);
   pBitmap->Clear(0);
   CFX_FloatRect cell_bbox = pPattern->bbox();
   pPattern->pattern_to_form()->TransformRect(cell_bbox);
   pObject2Device->TransformRect(cell_bbox);
   CFX_FloatRect bitmap_rect(0.0f, 0.0f, (FX_FLOAT)width, (FX_FLOAT)height);
   CFX_Matrix mtAdjust;
   mtAdjust.MatchRect(bitmap_rect, cell_bbox);
@@ skipping 377 matching lines @@
     }
   }
   if (bStroke) {
     const CPDF_Color& StrokeColor = *pPathObj->m_ColorState.GetStrokeColor();
     if (StrokeColor.IsPattern()) {
       DrawPathWithPattern(pPathObj, pObj2Device, &StrokeColor, TRUE);
       bStroke = FALSE;
     }
   }
 }