Adjust null object check

core/src/fpdfdoc/doc_ap.cpp

Index: core/src/fpdfdoc/doc_ap.cpp
diff --git a/core/src/fpdfdoc/doc_ap.cpp b/core/src/fpdfdoc/doc_ap.cpp
index 6a8ab374d21e7150339d2f4258977eef8b25c6d6..0e2a75ad2c90f7f9ff2013370a12234aacbdd54b 100644
--- a/core/src/fpdfdoc/doc_ap.cpp
+++ b/core/src/fpdfdoc/doc_ap.cpp
@@ -253,7 +253,10 @@ static FX_BOOL GenerateWidgetAP(CPDF_Document* pDoc, CPDF_Dictionary* pAnnotDict
     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");
     }