Remove "this==NULL" and adjust corresponding callers

fpdfsdk/src/formfiller/FFL_CBA_Fontmap.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/formfiller/FormFiller.h"
 #include "../../include/formfiller/FFL_CBA_Fontmap.h"
 
 CBA_FontMap::CBA_FontMap(CPDFSDK_Annot* pAnnot, IFX_SystemHandler* pSystemHandler) :
@@ skipping 221 matching lines @@
 
         FX_BOOL bWidget = (m_pAnnotDict->GetString("Subtype") == "Widget");
 
         if (bWidget)
         {
                 if (CPDF_Dictionary * pRootDict = m_pDocument->GetRoot())
                         pAcroFormDict = pRootDict->GetDict("AcroForm");
         }
         
         CFX_ByteString sDA;
-        
-        sDA = FPDF_GetFieldAttr(m_pAnnotDict, "DA")->GetString();
+        CPDF_Object* pObj;
+        if ((pObj = FPDF_GetFieldAttr(m_pAnnotDict, "DA")))
+                sDA = pObj->GetString();
 
         if (bWidget)
         {
                 if (sDA.IsEmpty())
                 {
-                        sDA = FPDF_GetFieldAttr(pAcroFormDict, "DA")->GetString();      
+                        pObj = FPDF_GetFieldAttr(pAcroFormDict, "DA");
+                        sDA = pObj ? pObj->GetString() : CFX_ByteString();
                 }
         }
         
         CPDF_Dictionary * pFontDict = NULL;     
 
         if (!sDA.IsEmpty())
         {
                 CPDF_SimpleParser syntax(sDA);
                 syntax.FindTagParam("Tf", 2);
                 CFX_ByteString sFontName = syntax.GetWord();
@@ skipping 31 matching lines @@
 }
 
 void CBA_FontMap::SetAPType(const CFX_ByteString& sAPType)
 {
         m_sAPType = sAPType;
 
         Reset();
         Initial();
 }