Adjust null object check

core/src/fpdfdoc/doc_ap.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/fpdfdoc/fpdf_doc.h"
 #include "../../include/fpdfdoc/fpdf_vt.h"
 #include "pdf_vt.h"
 #include "../../include/fpdfdoc/fpdf_ap.h"
@@ skipping 235 matching lines @@
 }
 static FX_BOOL GenerateWidgetAP(CPDF_Document* pDoc, CPDF_Dictionary* pAnnotDict, const FX_INT32 & nWidgetType)
 {
     CPDF_Dictionary* pFormDict = NULL;
     if (CPDF_Dictionary * pRootDict = pDoc->GetRoot()) {
         pFormDict = pRootDict->GetDict("AcroForm");
     }
     if (!pFormDict) {
         return FALSE;
     }
-    CFX_ByteString DA = FPDF_GetFieldAttr(pAnnotDict, "DA") ? FPDF_GetFieldAttr(pAnnotDict, "DA")->GetString() : CFX_ByteString();
+    CFX_ByteString DA;
+    if (CPDF_Object* pDAObj = FPDF_GetFieldAttr(pAnnotDict, "DA")) {
+        DA = pDAObj->GetString();
+    }
     if (DA.IsEmpty()) {
         DA = pFormDict->GetString("DA");
     }
     if (DA.IsEmpty()) {
         return FALSE;
     }
     CPDF_SimpleParser syntax(DA);
     syntax.FindTagParam("Tf", 2);
     CFX_ByteString sFontName = syntax.GetWord();
     sFontName = PDF_NameDecode(sFontName);
@@ skipping 532 matching lines @@
         case CT_GRAY:
             sColorStream << color.fColor1 << " " << (bFillOrStroke ? "g" : "G") << "\n";
             break;
         case CT_CMYK:
             sColorStream << color.fColor1 << " " << color.fColor2 << " " << color.fColor3 << " " << color.fColor4 << " "
                          << (bFillOrStroke ? "k" : "K") << "\n";
             break;
     }
     return sColorStream.GetByteString();
 }