commit a53e0641365608f832b455404f1ee584d278e0c4
Author: Albert Astals Cid <aacid@kde.org>
Date:   Sun Aug 5 15:07:16 2012 +0200

    If NULL, NULL fails as password try EMPTY, EMPTY before failing
    
    Reviewed by Jose Aliste
    Bug #3498

diff --git a/poppler/SecurityHandler.cc b/poppler/SecurityHandler.cc
index 00c4ae1..a48449a 100644
--- a/poppler/SecurityHandler.cc
+++ b/poppler/SecurityHandler.cc
@@ -105,7 +105,12 @@ GBool SecurityHandler::checkEncryption(GooString *ownerPassword,
     }
   }
   if (!ok) {
-    error(errCommandLine, -1, "Incorrect password");
+    if (!ownerPassword && !userPassword) {
+      GooString dummy;
+      return checkEncryption(&dummy, &dummy);
+    } else {
+      error(errCommandLine, -1, "Incorrect password");
+    }
   }
   return ok;
 }