#405 check encryption token value for null

src/UglyToad.PdfPig.Tests/Tokenization/Scanner/PdfTokenScannerTests.cs

@@ -417,6 +417,35 @@ endobj";
             Assert.Equal(3, third.Number.ObjectNumber);
         }
 
+        [Fact]
+        public void ReadsDictionaryContainingNull()
+        {
+            const string input = @"14224 0 obj
+<</Type /XRef
+/Root 8 0 R
+/Prev 116
+/Length 84
+/Size 35
+/W [1 3 2]
+/Index [0 1 6 1 8 2 25 10]
+/ID [ (ù¸7<C2B8>ãA×<41>žòÜ4<C39C><34>Š•)]
+/Info 6 0 R
+/Encrypt null>>
+endobj";
+
+            var scanner = GetScanner(input);
+
+            var tokens = ReadToEnd(scanner);
+
+            var dictionaryToken = tokens[0].Data as DictionaryToken;
+
+            Assert.NotNull(dictionaryToken);
+
+            var encryptValue = dictionaryToken.Data["Encrypt"];
+
+            Assert.IsType<NullToken>(encryptValue);
+        }
+
         private static PdfTokenScanner GetScanner(string s, TestObjectLocationProvider locationProvider = null)
         {
             var input = StringBytesTestConverter.Convert(s, false);

src/UglyToad.PdfPig/Parser/PdfDocumentFactory.cs

@@ -162,17 +162,7 @@
         private static (IndirectReference, DictionaryToken) ParseTrailer(CrossReferenceTable crossReferenceTable, bool isLenientParsing, IPdfTokenScanner pdfTokenScanner,
             out EncryptionDictionary encryptionDictionary)
         {
-            encryptionDictionary = null;
+            encryptionDictionary = GetEncryptionDictionary(crossReferenceTable, pdfTokenScanner);
-
-            if (crossReferenceTable.Trailer.EncryptionToken != null)
-            {
-                if (!DirectObjectFinder.TryGet(crossReferenceTable.Trailer.EncryptionToken, pdfTokenScanner, out DictionaryToken encryptionDictionaryToken))
-                {
-                    throw new PdfDocumentFormatException($"Unrecognized encryption token in trailer: {crossReferenceTable.Trailer.EncryptionToken}.");
-                }
-
-                encryptionDictionary = EncryptionDictionaryFactory.Read(encryptionDictionaryToken, pdfTokenScanner);
-            }
 
             var rootDictionary = DirectObjectFinder.Get<DictionaryToken>(crossReferenceTable.Trailer.Root, pdfTokenScanner);
 
@@ -183,5 +173,28 @@
 
             return (crossReferenceTable.Trailer.Root, rootDictionary);
         }
+
+        private static EncryptionDictionary GetEncryptionDictionary(CrossReferenceTable crossReferenceTable, IPdfTokenScanner pdfTokenScanner)
+        {
+            if (crossReferenceTable.Trailer.EncryptionToken == null)
+            {
+                return null;
+            }
+
+
+            if (!DirectObjectFinder.TryGet(crossReferenceTable.Trailer.EncryptionToken, pdfTokenScanner, out DictionaryToken encryptionDictionaryToken))
+            {
+                if (DirectObjectFinder.TryGet(crossReferenceTable.Trailer.EncryptionToken, pdfTokenScanner, out NullToken _))
+                {
+                    return null;
+                }
+
+                throw new PdfDocumentFormatException($"Unrecognized encryption token in trailer: {crossReferenceTable.Trailer.EncryptionToken}.");
+            }
+
+            var result = EncryptionDictionaryFactory.Read(encryptionDictionaryToken, pdfTokenScanner);
+
+            return result;
+        }
     }
 }