Remove "this==NULL" and adjust corresponding callers

core/src/fpdfapi/fpdf_render/fpdf_render_image.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 "../../../include/fxge/fx_ge.h"
 #include "../../../include/fxcodec/fx_codec.h"
 #include "../../../include/fpdfapi/fpdf_module.h"
 #include "../../../include/fpdfapi/fpdf_render.h"
@@ skipping 1064 matching lines @@
         return NULL;
     }
 #endif
     CFX_DIBitmap& bitmap = *bitmap_device.GetBitmap();
     CPDF_Object* pCSObj = NULL;
     CPDF_ColorSpace* pCS = NULL;
     if (bLuminosity) {
         CPDF_Array* pBC = pSMaskDict->GetArray(FX_BSTRC("BC"));
         FX_ARGB back_color = 0xff000000;
         if (pBC) {
-            pCSObj = pGroup->GetDict()->GetDict(FX_BSTRC("Group"))->GetElementValue(FX_BSTRC("CS"));
+            CPDF_Dictionary* pDict = pGroup->GetDict();
+            if (pDict && pDict->GetDict(FX_BSTRC("Group")))
+                pCSObj = pDict->GetDict(FX_BSTRC("Group"))->GetElementValue(FX_BSTRC("CS"));
+            else
+                pCSObj = NULL;
             pCS = m_pContext->m_pDocument->LoadColorSpace(pCSObj);
             if (pCS) {
                 FX_FLOAT R, G, B;
                 FX_DWORD num_floats = 8;
                 if (pCS->CountComponents() > (FX_INT32)num_floats) {
                     num_floats = (FX_DWORD)pCS->CountComponents();
                 }
                 CFX_FixedBufGrow<FX_FLOAT, 8> float_array(num_floats);
                 FX_FLOAT* pFloats = float_array;
                 FXSYS_memset32(pFloats, 0, num_floats * sizeof(FX_FLOAT));
@@ skipping 60 matching lines @@
         }
     } else {
         FXSYS_memcpy32(dest_buf, src_buf, dest_pitch * height);
     }
     if (pFunc) {
         delete pFunc;
     }
     FX_Free(pTransfer);
     return pMask;
 }