Fix usage of Empty field and Guid constructor from string (#244)

Author: josesimoes

Tests/NFUnitTestSystemLib/UnitTestGuid.cs

@@ -437,5 +437,24 @@ public void ToByteArray()
 
             CollectionAssert.AreEqual(new byte[] { 0xd5, 0x10, 0xa1, 0xa8, 0x49, 0xfc, 0xc5, 0x43, 0xbf, 0x46, 0x80, 0x2d, 0xb8, 0xf8, 0x43, 0xff }, myGuidAsArray);
         }
+
+        [TestMethod]
+        public void GuidAsStaticField()
+        {
+            var guid1 = ClassWithGuid.BaseUuid1;
+            var guid2 = ClassWithGuid.BaseUuid2;
+
+            Assert.AreEqual(new Guid("00000000-0000-1000-8000-00805f9b34fb"), guid1);
+            CollectionAssert.AreEqual(new byte[] { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x10, 0x80, 0x00, 0x00, 0x80, 0x5F, 0x9B, 0x34, 0xFB }, guid2);
+        }
+
+        internal class ClassWithGuid
+        {
+            private static Guid baseUuid1 = new Guid("00000000-0000-1000-8000-00805f9b34fb");
+            private static byte[] baseUuid2 = new Guid("00000000-0000-1000-8000-00805f9b34fb").ToByteArray();
+
+            public static Guid BaseUuid1 => baseUuid1;
+            public static byte[] BaseUuid2 => baseUuid2;
+        }
     }
 }

nanoFramework.CoreLibrary/System/AssemblyInfo.cs

@@ -10,4 +10,4 @@
 [assembly: AssemblyProduct(".NET nanoFramework mscorlib")]
 [assembly: AssemblyCopyright("Copyright (c) .NET Foundation and Contributors")]
 
-[assembly: AssemblyNativeVersion("100.5.0.23")]
+[assembly: AssemblyNativeVersion("100.5.0.24")]

nanoFramework.CoreLibrary/System/Guid.cs

@@ -16,18 +16,7 @@ public struct Guid
         /// <summary>
         /// A read-only instance of the Guid class which consists of all zeros.
         /// </summary>
-        public static readonly Guid Empty = new Guid(
-            0,
-            0,
-            0,
-            0,
-            0,
-            0,
-            0,
-            0,
-            0,
-            0,
-            0);
+        public static readonly Guid Empty = new Guid(new byte[16]);
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Guid"/> structure by using the specified integers and bytes.
@@ -154,13 +143,12 @@ public Guid(string g)
 #pragma warning disable S3928 // Parameter names used into ArgumentException constructors should match an existing one 
             if (!TryParseGuidWithDashes(
                 g,
-                out Guid result))
+                out this))
             {
                 throw new ArgumentException();
             }
 #pragma warning restore S3928 // Parameter names used into ArgumentException constructors should match an existing one
 
-            this = result;
         }
 
         /// <summary>
@@ -343,7 +331,7 @@ public static bool TryParseGuidWithDashes(
 
             // because this is a struct we can't assign the Empty directly to result,
             // otherwise it will overwrite the _data field of the struct, as this is a shallow copy
-            result = new Guid(Empty.ToByteArray());
+            result = new Guid(new byte[16]);
 
             // Check for optional surrounding braces
             if (input[0] == '{')