Adjust null object check

BUG=None
R=thakis@chromium.org

Review URL: https://codereview.chromium.org/396173003

core/src/fpdfdoc/doc_ap.cpp

diff --git a/core/src/fpdfdoc/doc_ap.cpp b/core/src/fpdfdoc/doc_ap.cpp
index 6a8ab37..0e2a75a 100644
--- a/core/src/fpdfdoc/doc_ap.cpp
+++ b/core/src/fpdfdoc/doc_ap.cpp
@@ -253,7 +253,10 @@
     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");
     }

core/src/fpdfdoc/doc_formfield.cpp

diff --git a/core/src/fpdfdoc/doc_formfield.cpp b/core/src/fpdfdoc/doc_formfield.cpp
index e51acf9..eeba372 100644
--- a/core/src/fpdfdoc/doc_formfield.cpp
+++ b/core/src/fpdfdoc/doc_formfield.cpp
@@ -1077,9 +1077,12 @@
 }
 void CPDF_FormField::LoadDA()
 {
-    CFX_ByteString DA = FPDF_GetFieldAttr(m_pDict, "DA") ? FPDF_GetFieldAttr(m_pDict, "DA")->GetString() : CFX_ByteString();
-    if (DA.IsEmpty()) {
-        DA = m_pForm->m_pFormDict ? m_pForm->m_pFormDict->GetString("DA") : CFX_ByteString();
+    CFX_ByteString DA;
+    if (CPDF_Object* pObj_t = FPDF_GetFieldAttr(m_pDict, "DA")) {
+        DA = pObj_t->GetString();
+    }
+    if (DA.IsEmpty() && m_pForm->m_pFormDict) {
+        DA = m_pForm->m_pFormDict->GetString("DA");
     }
     if (DA.IsEmpty()) {
         return;