CPDF_Document::LoadPattern() and friends always have a valid matrix.

core/fpdfapi/fpdf_page/cpdf_form.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/fpdfapi/fpdf_page/include/cpdf_form.h"
 
 #include "core/fpdfapi/fpdf_page/include/cpdf_pageobject.h"
 #include "core/fpdfapi/fpdf_page/include/cpdf_pageobjectholder.h"
 #include "core/fpdfapi/fpdf_page/pageint.h"
 #include "core/fpdfapi/fpdf_parser/include/cpdf_dictionary.h"
 #include "core/fpdfapi/fpdf_parser/include/cpdf_stream.h"
 
 CPDF_Form::CPDF_Form(CPDF_Document* pDoc,
                      CPDF_Dictionary* pPageResources,
                      CPDF_Stream* pFormStream,
                      CPDF_Dictionary* pParentResources) {
   m_pDocument = pDoc;
   m_pFormStream = pFormStream;
-  m_pFormDict = pFormStream ? pFormStream->GetDict() : NULL;
+  m_pFormDict = pFormStream ? pFormStream->GetDict() : nullptr;
   m_pResources = m_pFormDict->GetDictBy("Resources");
   m_pPageResources = pPageResources;
-  if (!m_pResources) {
+  if (!m_pResources)
     m_pResources = pParentResources;
-  }
-  if (!m_pResources) {
+  if (!m_pResources)
     m_pResources = pPageResources;
-  }
   m_Transparency = 0;
   LoadTransInfo();
 }
 
 CPDF_Form::~CPDF_Form() {}
 
 void CPDF_Form::StartParse(CPDF_AllStates* pGraphicStates,
-                           CFX_Matrix* pParentMatrix,
+                           const CFX_Matrix* pParentMatrix,
                            CPDF_Type3Char* pType3Char,
                            int level) {
-  if (m_ParseState == CONTENT_PARSED || m_ParseState == CONTENT_PARSING) {
+  if (m_ParseState == CONTENT_PARSED || m_ParseState == CONTENT_PARSING)
     return;
-  }
+
   m_pParser.reset(new CPDF_ContentParser);
   m_pParser->Start(this, pGraphicStates, pParentMatrix, pType3Char, level);
   m_ParseState = CONTENT_PARSING;
 }
 
 void CPDF_Form::ParseContent(CPDF_AllStates* pGraphicStates,
-                             CFX_Matrix* pParentMatrix,
+                             const CFX_Matrix* pParentMatrix,
                              CPDF_Type3Char* pType3Char,
                              int level) {
   StartParse(pGraphicStates, pParentMatrix, pType3Char, level);
-  ContinueParse(NULL);
+  ContinueParse(nullptr);
 }
 
 CPDF_Form* CPDF_Form::Clone() const {
   CPDF_Form* pCloneForm =
       new CPDF_Form(m_pDocument, m_pPageResources, m_pFormStream, m_pResources);
   for (const auto& pObj : m_PageObjectList)
     pCloneForm->m_PageObjectList.emplace_back(pObj->Clone());
 
   return pCloneForm;
 }