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

core/fpdfdoc/cpdf_annotlist.cpp

 // Copyright 2016 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/fpdfdoc/cpdf_annotlist.h"
 
 #include <memory>
 #include <utility>
 
 #include "core/fpdfapi/page/cpdf_page.h"
 #include "core/fpdfapi/parser/cpdf_document.h"
 #include "core/fpdfapi/parser/cpdf_reference.h"
 #include "core/fpdfapi/render/cpdf_renderoptions.h"
 #include "core/fpdfdoc/cpdf_annot.h"
 #include "core/fpdfdoc/cpdf_interform.h"
 #include "core/fpdfdoc/cpdf_occontext.h"
 #include "core/fpdfdoc/cpvt_generateap.h"
 #include "core/fxge/cfx_renderdevice.h"
 
 namespace {
 
 std::unique_ptr<CPDF_Annot> CreatePopupAnnot(CPDF_Annot* pAnnot,
                                              CPDF_Document* pDocument) {
   CPDF_Dictionary* pParentDict = pAnnot->GetAnnotDict();
   if (!pParentDict)
-    return std::unique_ptr<CPDF_Annot>();
+    return nullptr;
 
   // TODO(jaepark): We shouldn't strip BOM for some strings and not for others.
   // See pdfium:593.
   CFX_WideString sContents = pParentDict->GetUnicodeTextFor("Contents");
   if (sContents.IsEmpty())
-    return std::unique_ptr<CPDF_Annot>();
+    return nullptr;
 
   CPDF_Dictionary* pAnnotDict =
       new CPDF_Dictionary(pDocument->GetByteStringPool());
   pAnnotDict->SetNameFor("Type", "Annot");
   pAnnotDict->SetNameFor("Subtype", "Popup");
   pAnnotDict->SetStringFor("T", pParentDict->GetStringFor("T"));
   pAnnotDict->SetStringFor("Contents", sContents.UTF8Encode());
 
   CFX_FloatRect rect = pParentDict->GetRectFor("Rect");
   rect.Normalize();
@@ skipping 125 matching lines @@
                                    CPDF_RenderContext* pContext,
                                    FX_BOOL bPrinting,
                                    CFX_Matrix* pMatrix,
                                    FX_BOOL bShowWidget,
                                    CPDF_RenderOptions* pOptions) {
   uint32_t dwAnnotFlags = bShowWidget ? ANNOTFLAG_INVISIBLE | ANNOTFLAG_HIDDEN
                                       : ANNOTFLAG_INVISIBLE;
   DisplayAnnots(pPage, nullptr, pContext, bPrinting, pMatrix, dwAnnotFlags,
                 pOptions, nullptr);
 }