Enable explicit null checking of reference types

appveyor.yml

@@ -1,5 +1,5 @@
 version: '{build}'
-image: Visual Studio 2017
+image: Visual Studio 2019
 configuration:
 - Debug
 - Release

src/ICSharpCode.SharpZipLib/BZip2/BZip2Exception.cs

@@ -20,7 +20,7 @@ public BZip2Exception()
 		/// Initialise a new instance of <see cref="BZip2Exception" /> with its message string.
 		/// </summary>
 		/// <param name="message">A <see cref="string"/> that describes the error.</param>
-		public BZip2Exception(string message)
+		public BZip2Exception(string? message)
 			: base(message)
 		{
 		}
@@ -30,7 +30,7 @@ public BZip2Exception(string message)
 		/// </summary>
 		/// <param name="message">A <see cref="string"/> that describes the error.</param>
 		/// <param name="innerException">The <see cref="Exception"/> that caused this exception.</param>
-		public BZip2Exception(string message, Exception innerException)
+		public BZip2Exception(string? message, Exception? innerException)
 			: base(message, innerException)
 		{
 		}
@@ -46,7 +46,7 @@ public BZip2Exception(string message, Exception innerException)
 		/// The System.Runtime.Serialization.StreamingContext that contains contextual information
 		/// about the source or destination.
 		/// </param>
-		protected BZip2Exception(SerializationInfo info, StreamingContext context)
+		protected BZip2Exception(SerializationInfo? info, StreamingContext context)
 			: base(info, context)
 		{
 		}

src/ICSharpCode.SharpZipLib/BZip2/BZip2InputStream.cs

@@ -1,6 +1,7 @@
 using ICSharpCode.SharpZipLib.Checksum;
 using System;
 using System.IO;
+using ICSharpCode.SharpZipLib.Core;
 
 namespace ICSharpCode.SharpZipLib.BZip2
 {
@@ -9,7 +10,7 @@ namespace ICSharpCode.SharpZipLib.BZip2
 	/// </summary>
 	public class BZip2InputStream : Stream
 	{
-		#region Constants
+#region Constants
 
 		private const int START_BLOCK_STATE = 1;
 		private const int RAND_PART_A_STATE = 2;
@@ -19,9 +20,9 @@ public class BZip2InputStream : Stream
 		private const int NO_RAND_PART_B_STATE = 6;
 		private const int NO_RAND_PART_C_STATE = 7;
 
-		#endregion Constants
+#endregion Constants
 
-		#region Instance Fields
+#region Instance Fields
 
 		/*--
 		index of the last char in the block, so
@@ -55,8 +56,8 @@ The current block size is 100000 * this number.
 		private byte[] selector = new byte[BZip2Constants.MaximumSelectors];
 		private byte[] selectorMtf = new byte[BZip2Constants.MaximumSelectors];
 
-		private int[] tt;
-		private byte[] ll8;
+		private int[] tt = EmptyRefs.Int32Array;
+		private byte[] ll8 = EmptyRefs.ByteArray;
 
 		/*--
 		freq table collected to save a pass over the data
@@ -87,7 +88,7 @@ during decompression.
 		private int i2, j2;
 		private byte z;
 
-		#endregion Instance Fields
+#endregion Instance Fields
 
 		/// <summary>
 		/// Construct instance for reading from stream
@@ -119,7 +120,7 @@ public BZip2InputStream(Stream stream)
 		/// </summary>
 		public bool IsStreamOwner { get; set; } = true;
 
-		#region Stream Overrides
+#region Stream Overrides
 
 		/// <summary>
 		/// Gets a value indicating if the stream supports reading
@@ -222,7 +223,7 @@ public override void SetLength(long value)
 		/// <param name="offset">The offset to start obtaining data from.</param>
 		/// <param name="count">The number of bytes of data to write.</param>
 		/// <exception cref="NotSupportedException">Any access</exception>
-		public override void Write(byte[] buffer, int offset, int count)
+		public override void Write(byte[]? buffer, int offset, int count)
 		{
 			throw new NotSupportedException("BZip2InputStream Write not supported");
 		}
@@ -316,7 +317,7 @@ public override int ReadByte()
 			return retChar;
 		}
 
-		#endregion Stream Overrides
+#endregion Stream Overrides
 
 		private void MakeMaps()
 		{
@@ -746,7 +747,7 @@ cache misses.
 
 		private void SetupBlock()
 		{
-			int[] cftab = new int[257];
+			int[]? cftab = new int[257];
 
 			cftab[0] = 0;
 			Array.Copy(unzftab, 0, cftab, 1, 256);

src/ICSharpCode.SharpZipLib/BZip2/BZip2OutputStream.cs

@@ -1,6 +1,7 @@
 using ICSharpCode.SharpZipLib.Checksum;
 using System;
 using System.IO;
+using ICSharpCode.SharpZipLib.Core;
 
 namespace ICSharpCode.SharpZipLib.BZip2
 {
@@ -79,11 +80,11 @@ The current block size is 100000 * this number.
 		private char[] selector = new char[BZip2Constants.MaximumSelectors];
 		private char[] selectorMtf = new char[BZip2Constants.MaximumSelectors];
 
-		private byte[] block;
-		private int[] quadrant;
-		private int[] zptr;
-		private short[] szptr;
-		private int[] ftab;
+		private byte[] block = EmptyRefs.ByteArray;
+		private int[] quadrant = EmptyRefs.Int32Array;
+		private int[] zptr = EmptyRefs.Int32Array;
+		private short[] szptr = EmptyRefs.Int16Array;
+		private int[] ftab = EmptyRefs.Int32Array;
 
 		private int nMTF;
 
@@ -266,7 +267,7 @@ public override int ReadByte()
 		/// <returns>The total number of bytes read. This might be less than the number of bytes
 		/// requested if that number of bytes are not currently available, or zero
 		/// if the end of the stream is reached.</returns>
-		public override int Read(byte[] buffer, int offset, int count)
+		public override int Read(byte[]? buffer, int offset, int count)
 		{
 			throw new NotSupportedException("BZip2OutputStream Read not supported");
 		}
@@ -710,14 +711,14 @@ private void SendMTFValues()
 				remF -= aFreq;
 			}
 
-			int[][] rfreq = new int[BZip2Constants.GroupCount][];
+			int[][]? rfreq = new int[BZip2Constants.GroupCount][];
 			for (int i = 0; i < BZip2Constants.GroupCount; ++i)
 			{
 				rfreq[i] = new int[BZip2Constants.MaximumAlphaSize];
 			}
 
-			int[] fave = new int[BZip2Constants.GroupCount];
-			short[] cost = new short[BZip2Constants.GroupCount];
+			int[]? fave = new int[BZip2Constants.GroupCount];
+			short[]? cost = new short[BZip2Constants.GroupCount];
 			/*---
 			Iterate up to N_ITERS times to improve the tables.
 			---*/
@@ -1691,7 +1692,7 @@ private void AllocateCompressStructures()
 			zptr = new int[n];
 			ftab = new int[65537];
 
-			if (block == null || quadrant == null || zptr == null || ftab == null)
+			if (block == EmptyRefs.ByteArray || quadrant == null || zptr == null || ftab == null)
 			{
 				//		int totalDraw = (n + 1 + NUM_OVERSHOOT_BYTES) + (n + NUM_OVERSHOOT_BYTES) + n + 65537;
 				//		compressOutOfMemory ( totalDraw, n );

src/ICSharpCode.SharpZipLib/Core/EmptyRefs.cs

@@ -0,0 +1,22 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using ICSharpCode.SharpZipLib.Zip;
+
+namespace ICSharpCode.SharpZipLib.Core
+{
+	internal static class EmptyRefs
+	{
+#if NET45
+		public static byte[] ByteArray { get; } = new byte[0];
+		public static int[] Int32Array { get; } = new int[0];
+		public static short[] Int16Array {get; } = new short[0];
+		public static ZipEntry[] ZipEntryArray { get; } = new ZipEntry[0];
+#else
+		public static byte[] ByteArray => Array.Empty<byte>(); 
+		public static int[] Int32Array => Array.Empty<int>();
+		public static short[] Int16Array => Array.Empty<short>();
+		public static ZipEntry[] ZipEntryArray => Array.Empty<ZipEntry>();
+#endif
+	}
+}

src/ICSharpCode.SharpZipLib/Core/Exceptions/SharpZipBaseException.cs

@@ -23,7 +23,7 @@ public SharpZipBaseException()
 		/// Initializes a new instance of the SharpZipBaseException class with a specified error message.
 		/// </summary>
 		/// <param name="message">A message describing the exception.</param>
-		public SharpZipBaseException(string message)
+		public SharpZipBaseException(string? message)
 			: base(message)
 		{
 		}
@@ -34,7 +34,7 @@ public SharpZipBaseException(string message)
 		/// </summary>
 		/// <param name="message">A message describing the exception.</param>
 		/// <param name="innerException">The inner exception</param>
-		public SharpZipBaseException(string message, Exception innerException)
+		public SharpZipBaseException(string? message, Exception? innerException)
 			: base(message, innerException)
 		{
 		}
@@ -50,7 +50,7 @@ public SharpZipBaseException(string message, Exception innerException)
 		/// The System.Runtime.Serialization.StreamingContext that contains contextual information
 		/// about the source or destination.
 		/// </param>
-		protected SharpZipBaseException(SerializationInfo info, StreamingContext context)
+		protected SharpZipBaseException(SerializationInfo? info, StreamingContext context)
 			: base(info, context)
 		{
 		}

src/ICSharpCode.SharpZipLib/Core/Exceptions/StreamDecodingException.cs

@@ -21,15 +21,15 @@ public StreamDecodingException() : base(GenericMessage) { }
 		/// Initializes a new instance of the StreamDecodingException class with a specified error message.
 		/// </summary>
 		/// <param name="message">A message describing the exception.</param>
-		public StreamDecodingException(string message) : base(message) { }
+		public StreamDecodingException(string? message) : base(message) { }
 
 		/// <summary>
 		/// Initializes a new instance of the StreamDecodingException class with a specified
 		/// error message and a reference to the inner exception that is the cause of this exception.
 		/// </summary>
 		/// <param name="message">A message describing the exception.</param>
 		/// <param name="innerException">The inner exception</param>
-		public StreamDecodingException(string message, Exception innerException) : base(message, innerException) { }
+		public StreamDecodingException(string? message, Exception? innerException) : base(message, innerException) { }
 
 		/// <summary>
 		/// Initializes a new instance of the StreamDecodingException class with serialized data.
@@ -42,7 +42,7 @@ public StreamDecodingException(string message, Exception innerException) : base(
 		/// The System.Runtime.Serialization.StreamingContext that contains contextual information
 		/// about the source or destination.
 		/// </param>
-		protected StreamDecodingException(SerializationInfo info, StreamingContext context)
+		protected StreamDecodingException(SerializationInfo? info, StreamingContext context)
 			: base(info, context)
 		{
 		}

src/ICSharpCode.SharpZipLib/Core/Exceptions/StreamUnsupportedException.cs

@@ -20,15 +20,15 @@ public StreamUnsupportedException() : base(GenericMessage) { }
 		/// Initializes a new instance of the StreamUnsupportedException class with a specified error message.
 		/// </summary>
 		/// <param name="message">A message describing the exception.</param>
-		public StreamUnsupportedException(string message) : base(message) { }
+		public StreamUnsupportedException(string? message) : base(message) { }
 
 		/// <summary>
 		/// Initializes a new instance of the StreamUnsupportedException class with a specified
 		/// error message and a reference to the inner exception that is the cause of this exception.
 		/// </summary>
 		/// <param name="message">A message describing the exception.</param>
 		/// <param name="innerException">The inner exception</param>
-		public StreamUnsupportedException(string message, Exception innerException) : base(message, innerException) { }
+		public StreamUnsupportedException(string? message, Exception? innerException) : base(message, innerException) { }
 
 		/// <summary>
 		/// Initializes a new instance of the StreamUnsupportedException class with serialized data.
@@ -41,7 +41,7 @@ public StreamUnsupportedException(string message, Exception innerException) : ba
 		/// The System.Runtime.Serialization.StreamingContext that contains contextual information
 		/// about the source or destination.
 		/// </param>
-		protected StreamUnsupportedException(SerializationInfo info, StreamingContext context)
+		protected StreamUnsupportedException(SerializationInfo? info, StreamingContext context)
 			: base(info, context)
 		{
 		}

src/ICSharpCode.SharpZipLib/Core/Exceptions/UnexpectedEndOfStreamException.cs

@@ -20,15 +20,15 @@ public UnexpectedEndOfStreamException() : base(GenericMessage) { }
 		/// Initializes a new instance of the UnexpectedEndOfStreamException class with a specified error message.
 		/// </summary>
 		/// <param name="message">A message describing the exception.</param>
-		public UnexpectedEndOfStreamException(string message) : base(message) { }
+		public UnexpectedEndOfStreamException(string? message) : base(message) { }
 
 		/// <summary>
 		/// Initializes a new instance of the UnexpectedEndOfStreamException class with a specified
 		/// error message and a reference to the inner exception that is the cause of this exception.
 		/// </summary>
 		/// <param name="message">A message describing the exception.</param>
 		/// <param name="innerException">The inner exception</param>
-		public UnexpectedEndOfStreamException(string message, Exception innerException) : base(message, innerException) { }
+		public UnexpectedEndOfStreamException(string? message, Exception? innerException) : base(message, innerException) { }
 
 		/// <summary>
 		/// Initializes a new instance of the UnexpectedEndOfStreamException class with serialized data.
@@ -41,7 +41,7 @@ public UnexpectedEndOfStreamException(string message, Exception innerException)
 		/// The System.Runtime.Serialization.StreamingContext that contains contextual information
 		/// about the source or destination.
 		/// </param>
-		protected UnexpectedEndOfStreamException(SerializationInfo info, StreamingContext context)
+		protected UnexpectedEndOfStreamException(SerializationInfo? info, StreamingContext context)
 			: base(info, context)
 		{
 		}

src/ICSharpCode.SharpZipLib/Core/Exceptions/ValueOutOfRangeException.cs

@@ -13,7 +13,7 @@ public class ValueOutOfRangeException : StreamDecodingException
 		/// Initializes a new instance of the ValueOutOfRangeException class naming the causing variable
 		/// </summary>
 		/// <param name="nameOfValue">Name of the variable, use: nameof()</param>
-		public ValueOutOfRangeException(string nameOfValue)
+		public ValueOutOfRangeException(string? nameOfValue)
 			: base($"{nameOfValue} out of range") { }
 
 		/// <summary>
@@ -24,7 +24,7 @@ public ValueOutOfRangeException(string nameOfValue)
 		/// <param name="value">The invalid value</param>
 		/// <param name="maxValue">Expected maximum value</param>
 		/// <param name="minValue">Expected minimum value</param>
-		public ValueOutOfRangeException(string nameOfValue, long value, long maxValue, long minValue = 0)
+		public ValueOutOfRangeException(string? nameOfValue, long value, long maxValue, long minValue = 0)
 			: this(nameOfValue, value.ToString(), maxValue.ToString(), minValue.ToString()) { }
 
 		/// <summary>
@@ -35,15 +35,15 @@ public ValueOutOfRangeException(string nameOfValue, long value, long maxValue, l
 		/// <param name="value">The invalid value</param>
 		/// <param name="maxValue">Expected maximum value</param>
 		/// <param name="minValue">Expected minimum value</param>
-		public ValueOutOfRangeException(string nameOfValue, string value, string maxValue, string minValue = "0") :
+		public ValueOutOfRangeException(string? nameOfValue, string? value, string? maxValue, string? minValue = "0") :
 			base($"{nameOfValue} out of range: {value}, should be {minValue}..{maxValue}")
 		{ }
 
 		private ValueOutOfRangeException()
 		{
 		}
 
-		private ValueOutOfRangeException(string message, Exception innerException) : base(message, innerException)
+		private ValueOutOfRangeException(string? message, Exception? innerException) : base(message, innerException)
 		{
 		}
 
@@ -58,7 +58,7 @@ private ValueOutOfRangeException(string message, Exception innerException) : bas
 		/// The System.Runtime.Serialization.StreamingContext that contains contextual information
 		/// about the source or destination.
 		/// </param>
-		protected ValueOutOfRangeException(SerializationInfo info, StreamingContext context)
+		protected ValueOutOfRangeException(SerializationInfo? info, StreamingContext context)
 			: base(info, context)
 		{
 		}