Prefer is null to == null

ensures that an equals overload isn't use, and we don't compare structs

src/UglyToad.PdfPig/AcroForms/AcroFormFactory.cs

@@ -213,7 +213,7 @@ private AcroFieldBase GetAcroField(DictionaryToken fieldDictionary, Catalog cata
             var fieldFlags = (uint) (fieldFlagsToken?.Long ?? 0);
 
             AcroFieldBase result;
-            if (fieldType == null)
+            if (fieldType is null)
             {
                 result = new AcroNonTerminalField(fieldDictionary, "Non-Terminal Field", fieldFlags, information, AcroFieldType.Unknown, children);
             }
@@ -562,7 +562,7 @@ private static bool IsChoiceSelected(IReadOnlyList<string> selectedOptionNames,
                     continue;
                 }
 
-                if (selectedOptionIndices == null)
+                if (selectedOptionIndices is null)
                 {
                     return true;
                 }

src/UglyToad.PdfPig/AcroForms/Fields/AcroFieldCommonInformation.cs

@@ -50,7 +50,7 @@ public override string ToString()
         {
             string AppendIfNotNull(string val, string label, string result)
             {
-                if (val == null)
+                if (val is null)
                 {
                     return result;
                 }

src/UglyToad.PdfPig/Annotations/AppearanceStream.cs

@@ -53,7 +53,7 @@ internal AppearanceStream(IDictionary<string, StreamToken> appearanceStreamsBySt
         /// <exception cref="ArgumentOutOfRangeException"></exception>
         public StreamToken Get(string state)
         {
-            if (appearanceStreamsByState == null)
+            if (appearanceStreamsByState is null)
             {
                 throw new Exception("Cannot get appearance by state when this is a stateless appearance stream");
             }

src/UglyToad.PdfPig/Annotations/QuadPointsQuadrilateral.cs

@@ -23,7 +23,7 @@ public class QuadPointsQuadrilateral
         /// </summary>
         public QuadPointsQuadrilateral(IReadOnlyList<PdfPoint> points)
         {
-            if (points == null)
+            if (points is null)
             {
                 throw new ArgumentNullException(nameof(points));
             }

src/UglyToad.PdfPig/Content/BasePageFactory.cs

@@ -66,7 +66,7 @@ protected BasePageFactory(
         public TPage Create(int number, DictionaryToken dictionary, PageTreeMembers pageTreeMembers,
              NamedDestinations namedDestinations)
         {
-            if (dictionary == null)
+            if (dictionary is null)
             {
                 throw new ArgumentNullException(nameof(dictionary));
             }
@@ -131,7 +131,7 @@ public TPage Create(int number, DictionaryToken dictionary, PageTreeMembers page
 
                     var contentStream = DirectObjectFinder.Get<StreamToken>(obj, PdfScanner);
 
-                    if (contentStream == null)
+                    if (contentStream is null)
                     {
                         throw new InvalidOperationException($"Could not find the contents for object {obj}.");
                     }
@@ -150,7 +150,7 @@ public TPage Create(int number, DictionaryToken dictionary, PageTreeMembers page
             {
                 var contentStream = DirectObjectFinder.Get<StreamToken>(contents, PdfScanner);
 
-                if (contentStream == null)
+                if (contentStream is null)
                 {
                     throw new InvalidOperationException("Failed to parse the content for the page: " + number);
                 }
@@ -181,7 +181,7 @@ private TPage ProcessPageInternal(
         {
             IReadOnlyList<IGraphicsStateOperation> operations;
 
-            if (contentBytes == null || contentBytes.Count == 0)
+            if (contentBytes is null || contentBytes.Count == 0)
             {
                 operations = Array.Empty<IGraphicsStateOperation>();
             }
@@ -293,7 +293,7 @@ protected MediaBox GetMediaBox(int number, DictionaryToken dictionary, PageTreeM
             {
                 mediaBox = pageTreeMembers.MediaBox;
 
-                if (mediaBox == null)
+                if (mediaBox is null)
                 {
                     ParsingOptions.Logger.Error(
                         $"The MediaBox was the wrong missing for page {number}. Using US Letter.");

src/UglyToad.PdfPig/Content/DocumentInformation.cs

@@ -124,7 +124,7 @@ public override string ToString()
 
         private static void AppendPart(string name, string value, StringBuilder builder)
         {
-            if (value == null)
+            if (value is null)
             {
                 return;
             }

src/UglyToad.PdfPig/Content/InlineImage.cs

@@ -108,7 +108,7 @@ internal InlineImage(PdfRectangle bounds, int widthInSamples, int heightInSample
         public bool TryGetBytes(out IReadOnlyList<byte> bytes)
         {
             bytes = null;
-            if (bytesFactory == null)
+            if (bytesFactory is null)
             {
                 return false;
             }

src/UglyToad.PdfPig/Content/Page.cs

@@ -122,7 +122,7 @@ internal Page(int number, DictionaryToken dictionary, MediaBox mediaBox, CropBox
 
         private static string GetText(PageContent content)
         {
-            if (content?.Letters == null)
+            if (content?.Letters is null)
             {
                 return string.Empty;
             }

src/UglyToad.PdfPig/Content/PageTreeNode.cs

@@ -49,7 +49,7 @@ public class PageTreeNode
         /// <summary>
         /// Whether this node is the root node.
         /// </summary>
-        public bool IsRoot => Parent == null;
+        public bool IsRoot => Parent is null;
 
         /// <summary>
         /// Create a new <see cref="PageTreeNode"/>.

src/UglyToad.PdfPig/Content/Pages.cs

@@ -132,7 +132,7 @@ internal void AddPageFactory<TPage, TPageFactory>() where TPageFactory : IPageFa
                 typeof(ParsingOptions)
             });
 
-            if (constructor == null)
+            if (constructor is null)
             {
                 throw new InvalidOperationException($"Could not find valid constructor for page factory of type '{typeof(TPageFactory)}'. " +
                                                     "The page factory should have a constructor with the following parameters: " +

src/UglyToad.PdfPig/Content/ResourceStore.cs

@@ -200,7 +200,7 @@ private void LoadFontDictionary(DictionaryToken fontDictionary)
 
                     var fontObject = DirectObjectFinder.Get<DictionaryToken>(objectKey, scanner);
 
-                    if (fontObject == null)
+                    if (fontObject is null)
                     {
                         //This is a valid use case
                         continue;
@@ -269,7 +269,7 @@ public bool TryGetNamedColorSpace(NameToken name, out ResourceColorSpace namedTo
         {
             namedToken = default(ResourceColorSpace);
 
-            if (name == null)
+            if (name is null)
             {
                 throw new ArgumentNullException(nameof(name));
             }
@@ -286,7 +286,7 @@ public bool TryGetNamedColorSpace(NameToken name, out ResourceColorSpace namedTo
 
         public ColorSpaceDetails GetColorSpaceDetails(NameToken name, DictionaryToken dictionary)
         {
-            if (dictionary == null)
+            if (dictionary is null)
             {
                 dictionary = new DictionaryToken(new Dictionary<NameToken, IToken>());
             }

src/UglyToad.PdfPig/Content/Word.cs

@@ -42,7 +42,7 @@ public class Word
         /// <param name="letters">The letters contained in the word, in the correct order.</param>
         public Word(IReadOnlyList<Letter> letters)
         {
-            if (letters == null)
+            if (letters is null)
             {
                 throw new ArgumentNullException(nameof(letters));
             }

src/UglyToad.PdfPig/CrossReference/CrossReferenceTable.cs

@@ -44,7 +44,7 @@ internal CrossReferenceTable(CrossReferenceType type, IReadOnlyDictionary<Indire
             TrailerDictionary trailer,
             IReadOnlyList<CrossReferenceOffset> crossReferenceOffsets)
         {
-            if (objectOffsets == null)
+            if (objectOffsets is null)
             {
                 throw new ArgumentNullException(nameof(objectOffsets));
             }

src/UglyToad.PdfPig/CrossReference/CrossReferenceTableBuilder.cs

@@ -20,7 +20,7 @@ internal class CrossReferenceTableBuilder
 
         public void Add(CrossReferenceTablePart part)
         {
-            if (part == null)
+            if (part is null)
             {
                 throw new ArgumentNullException(nameof(part));
             }
@@ -38,7 +38,7 @@ public CrossReferenceTable Build(long firstCrossReferenceOffset, long offsetCorr
 
             var currentPart = parts.FirstOrDefault(x => x.Offset == firstCrossReferenceOffset);
 
-            if (currentPart == null)
+            if (currentPart is null)
             {
                 // no XRef at given position
                 log.Warn($"Did not find an XRef object at the specified startxref position {firstCrossReferenceOffset}");
@@ -73,7 +73,7 @@ public CrossReferenceTable Build(long firstCrossReferenceOffset, long offsetCorr
                     }
 
                     currentPart = parts.FirstOrDefault(x => x.Offset == prevBytePos || x.Offset == prevBytePos + offsetCorrection);
-                    if (currentPart == null)
+                    if (currentPart is null)
                     {
                         log.Warn("Did not found XRef object pointed to by 'Prev' key at position " + prevBytePos);
                         break;

src/UglyToad.PdfPig/CrossReference/TrailerDictionary.cs

@@ -56,7 +56,7 @@ public class TrailerDictionary
         /// <param name="dictionary">The parsed dictionary from the document.</param>
         internal TrailerDictionary(DictionaryToken dictionary)
         {
-            if (dictionary == null)
+            if (dictionary is null)
             {
                 throw new ArgumentNullException(nameof(dictionary));
             }

src/UglyToad.PdfPig/Encryption/CryptHandler.cs

@@ -15,12 +15,12 @@ internal class CryptHandler
         public CryptHandler(DictionaryToken cryptDictionary,
             NameToken streamName, NameToken stringName)
         {
-            if (streamName == null)
+            if (streamName is null)
             {
                 throw new ArgumentNullException(nameof(streamName));
             }
 
-            if (stringName == null)
+            if (stringName is null)
             {
                 throw new ArgumentNullException(nameof(stringName));
             }
@@ -32,7 +32,7 @@ public CryptHandler(DictionaryToken cryptDictionary,
 
         public CryptDictionary GetNamedCryptDictionary(NameToken name)
         {
-            if (name == null)
+            if (name is null)
             {
                 throw new ArgumentNullException(nameof(name));
             }

src/UglyToad.PdfPig/Encryption/EncryptionDictionaryFactory.cs

@@ -11,7 +11,7 @@ internal static class EncryptionDictionaryFactory
     {
         public static EncryptionDictionary Read(DictionaryToken encryptionDictionary, IPdfTokenScanner tokenScanner)
         {
-            if (encryptionDictionary == null)
+            if (encryptionDictionary is null)
             {
                 throw new ArgumentNullException(nameof(encryptionDictionary));
             }

src/UglyToad.PdfPig/Encryption/EncryptionHandler.cs

@@ -70,7 +70,7 @@ public EncryptionHandler(EncryptionDictionary encryptionDictionary, TrailerDicti
                 documentIdBytes = [];
             }
 
-            if (encryptionDictionary == null)
+            if (encryptionDictionary is null)
             {
                 return;
             }
@@ -329,7 +329,7 @@ private static bool IsOwnerPasswordRevision5And6(byte[] passwordBytes, Encryptio
 
         public IToken Decrypt(IndirectReference reference, IToken token)
         {
-            if (token == null)
+            if (token is null)
             {
                 throw new ArgumentNullException(nameof(token));
             }
@@ -728,7 +728,7 @@ private static void UpdateMd5(MD5 md5, byte[] data)
 
         private static byte[] GetPaddedPassword(byte[] password)
         {
-            if (password == null || password.Length == 0)
+            if (password is null || password.Length == 0)
             {
                 return PaddingBytes;
             }
@@ -771,7 +771,7 @@ private static byte[] TruncatePasswordTo127Bytes(byte[] password)
         private static byte[] ComputeStupidIsoHash(byte[] password, byte[] salt, byte[] vector)
         {
             // There are some details here https://web.archive.org/web/20180311160224/esec-lab.sogeti.com/posts/2011/09/14/the-undocumented-password-validation-algorithm-of-adobe-reader-x.html
-            if (vector == null)
+            if (vector is null)
             {
                 vector = [];
             }

src/UglyToad.PdfPig/Filters/CcittFaxDecoderStream.cs

@@ -115,7 +115,7 @@ private void Decode2D()
                 {
                     node = node.Walk(ReadBit());
 
-                    if (node == null)
+                    if (node is null)
                     {
                         goto mode;
                     }
@@ -224,7 +224,7 @@ private void DecodeRowType4()
                 {
                     node = node.Walk(ReadBit());
 
-                    if (node == null)
+                    if (node is null)
                     {
                         goto eof;
                     }
@@ -347,7 +347,7 @@ private int DecodeRun(Tree tree)
                 var bit = ReadBit();
                 node = node.Walk(bit);
 
-                if (node == null)
+                if (node is null)
                 {
                     throw new InvalidOperationException("Unknown code in Huffman RLE stream");
                 }
@@ -495,7 +495,7 @@ public void Fill(int depth, int path, int value)
                     var isSet = ((path >> bitPos) & 1) == 1;
                     var next = current.Walk(isSet);
 
-                    if (next == null)
+                    if (next is null)
                     {
                         next = new Node();
 
@@ -531,7 +531,7 @@ public void Fill(int depth, int path, Node node)
                     var isSet = ((path >> bitPos) & 1) == 1;
                     var next = current.Walk(isSet);
 
-                    if (next == null)
+                    if (next is null)
                     {
                         if (i == depth - 1)
                         {

src/UglyToad.PdfPig/Filters/DecodeParameterResolver.cs

@@ -9,7 +9,7 @@ internal static class DecodeParameterResolver
     {
         public static DictionaryToken GetFilterParameters(DictionaryToken streamDictionary, int index)
         {
-            if (streamDictionary == null)
+            if (streamDictionary is null)
             {
                 throw new ArgumentNullException(nameof(streamDictionary));
             }

src/UglyToad.PdfPig/Filters/DefaultFilterProvider.cs

@@ -56,13 +56,13 @@ private DefaultFilterProvider()
         /// <inheritdoc />
         public IReadOnlyList<IFilter> GetFilters(DictionaryToken dictionary)
         {
-            if (dictionary == null)
+            if (dictionary is null)
             {
                 throw new ArgumentNullException(nameof(dictionary));
             }
 
             var token = dictionary.GetObjectOrDefault(NameToken.Filter, NameToken.F);
-            if (token == null)
+            if (token is null)
             {
                 return Array.Empty<IFilter>();
             }
@@ -89,7 +89,7 @@ public IReadOnlyList<IFilter> GetFilters(DictionaryToken dictionary)
         /// <inheritdoc />
         public IReadOnlyList<IFilter> GetNamedFilters(IReadOnlyList<NameToken> names)
         {
-            if (names == null)
+            if (names is null)
             {
                 throw new ArgumentNullException(nameof(names));
             }

src/UglyToad.PdfPig/Filters/FilterProviderWithLookup.cs

@@ -29,13 +29,13 @@ public IReadOnlyList<IFilter> GetAllFilters()
 
         public IReadOnlyList<IFilter> GetFilters(DictionaryToken dictionary, IPdfTokenScanner scanner)
         {
-            if (dictionary == null)
+            if (dictionary is null)
             {
                 throw new ArgumentNullException(nameof(dictionary));
             }
 
             var token = dictionary.GetObjectOrDefault(NameToken.Filter, NameToken.F);
-            if (token == null)
+            if (token is null)
             {
                 return Array.Empty<IFilter>();
             }
@@ -57,7 +57,7 @@ public IReadOnlyList<IFilter> GetFilters(DictionaryToken dictionary, IPdfTokenSc
                 case IndirectReferenceToken irt:
                     if (DirectObjectFinder.TryGet<NameToken>(irt, scanner, out var indirectName))
                     {
-                        return GetNamedFilters(new []{ indirectName });
+                        return GetNamedFilters(new[] { indirectName });
                     }
                     else if (DirectObjectFinder.TryGet<ArrayToken>(irt, scanner, out var indirectArray))
                     {

src/UglyToad.PdfPig/Filters/FlateFilter.cs

@@ -36,7 +36,7 @@ internal class FlateFilter : IFilter
         /// <inheritdoc />
         public byte[] Decode(IReadOnlyList<byte> input, DictionaryToken streamDictionary, int filterIndex)
         {
-            if (input == null)
+            if (input is null)
             {
                 throw new ArgumentNullException(nameof(input));
             }