Merge PR #432: Throw ArgumentNullException in BZip2

Change the BZip2 Compress/Decompress functions to throw ArgumentNullxception rather than Exception when null stream parameters are provided

src/ICSharpCode.SharpZipLib/BZip2/BZip2.cs

@@ -17,10 +17,11 @@ public static class BZip2
 		/// <param name="isStreamOwner">Both streams are closed on completion if true.</param>
 		public static void Decompress(Stream inStream, Stream outStream, bool isStreamOwner)
 		{
-			if (inStream == null || outStream == null)
-			{
-				throw new Exception("Null Stream");
-			}
+			if (inStream == null)
+				throw new ArgumentNullException(nameof(inStream));
+
+			if (outStream == null)
+				throw new ArgumentNullException(nameof(outStream));
 
 			try
 			{
@@ -51,10 +52,11 @@ public static void Decompress(Stream inStream, Stream outStream, bool isStreamOw
 		/// the lowest compression and 9 the highest.</param>
 		public static void Compress(Stream inStream, Stream outStream, bool isStreamOwner, int level)
 		{
-			if (inStream == null || outStream == null)
-			{
-				throw new Exception("Null Stream");
-			}
+			if (inStream == null)
+				throw new ArgumentNullException(nameof(inStream));
+
+			if (outStream == null)
+				throw new ArgumentNullException(nameof(outStream));
 
 			try
 			{