Fix #2090: ignore mscorlib references without public key token, when trying to resolve mscorlib. This will automatically fallback to .NET 4.0's mscorlib.dll.

ICSharpCode.Decompiler/Metadata/MetadataExtensions.cs

@@ -95,6 +95,9 @@ namespace ICSharpCode.Decompiler.Metadata
 
 		public static string ToHexString(this IEnumerable<byte> bytes, int estimatedLength)
 		{
+			if (bytes == null)
+				throw new ArgumentNullException(nameof(bytes));
+
 			StringBuilder sb = new StringBuilder(estimatedLength * 2);
 			foreach (var b in bytes)
 				sb.AppendFormat("{0:x2}", b);

ICSharpCode.Decompiler/Metadata/UniversalAssemblyResolver.cs

@@ -398,6 +398,9 @@ namespace ICSharpCode.Decompiler.Metadata
 					return typeof(object).Module.FullyQualifiedName;
 			}
 
+			if (reference.PublicKeyToken == null)
+				return null;
+
 			string path;
 			if (decompilerRuntime == DecompilerRuntime.Mono) {
 				path = GetMonoMscorlibBasePath(version);