Fix NullableAttribute Issue (#1081)

* Fixed #1068 (NullableAttribute)

Source/Mosa.Korlib/System.Runtime.CompilerServices/NullableAttribute.cs

@@ -0,0 +1,35 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+//using System.ComponentModel;
+
+namespace System.Runtime.CompilerServices
+{
+	/// <summary>
+	/// Reserved for use by a compiler for tracking metadata.
+	/// This attribute should not be used by developers in source code.
+	/// </summary>
+	//[EditorBrowsable(EditorBrowsableState.Never)]
+	[AttributeUsage(AttributeTargets.Class | AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Event | AttributeTargets.Parameter | AttributeTargets.ReturnValue | AttributeTargets.GenericParameter, Inherited = false)]
+	public sealed class NullableAttribute : Attribute
+	{
+		/// <summary>Flags specifying metadata related to nullable reference types.</summary>
+		public readonly byte[] NullableFlags;
+
+		/// <summary>Initializes the attribute.</summary>
+		/// <param name="value">The flags value.</param>
+		public NullableAttribute(byte value)
+		{
+			NullableFlags = new[] { value };
+		}
+
+		/// <summary>Initializes the attribute.</summary>
+		/// <param name="value">The flags value.</param>
+		public NullableAttribute(byte[] value)
+		{
+			NullableFlags = value;
+		}
+	}
+}
+
+

Source/Mosa.UnitTests/Other/SpecificTests.cs

@@ -270,6 +270,20 @@ public static bool BranchingEqU8(ulong x, ulong y)
 		}
 		return result;
 	}
+
+	public static string str = null!;
+
+#nullable enable
+
+	[MosaUnitTest]
+	public static bool TestNullable()
+	{
+		str = "Hello!";
+
+		return string.IsNullOrEmpty(str);
+	}
+
+#nullable disable
 }
 
 public static class Extension