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

core/fpdfapi/fpdf_page/cpdf_pattern.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/cpdf_pattern.h"
 
 CPDF_Pattern::CPDF_Pattern(PatternType type,
                            CPDF_Document* pDoc,
                            CPDF_Object* pObj,
-                           const CFX_Matrix* pParentMatrix)
-    : m_PatternType(type), m_pDocument(pDoc), m_pPatternObj(pObj) {
-  if (pParentMatrix)
-    m_ParentMatrix = *pParentMatrix;
-}
+                           const CFX_Matrix& parentMatrix)
+    : m_PatternType(type),
+      m_pDocument(pDoc),
+      m_pPatternObj(pObj),
+      m_ParentMatrix(parentMatrix) {}
 
 CPDF_Pattern::~CPDF_Pattern() {}