bug #6: 0 and 17 are illegal values for PrimitiveType enum

Author: adamsitnik

src/libraries/System.Formats.Nrbf/src/System/Formats/Nrbf/Utils/BinaryReaderExtensions.cs

@@ -61,7 +61,7 @@ internal static PrimitiveType ReadPrimitiveType(this BinaryReader reader)
     {
         byte primitiveType = reader.ReadByte();
         // String is the last defined value, 4 is not used at all.
-        if (primitiveType is 4 or > (byte)PrimitiveType.String)
+        if (primitiveType is 0 or 4 or (byte)PrimitiveType.Null or > (byte)PrimitiveType.String)
         {
             ThrowHelper.ThrowInvalidValue(primitiveType);
         }

src/libraries/System.Formats.Nrbf/tests/InvalidInputTests.cs

@@ -426,7 +426,9 @@ public static IEnumerable<object[]> ThrowsForInvalidPrimitiveType_Arguments()
         {
             foreach (byte binaryType in new byte[] { (byte)0 /* BinaryType.Primitive */, (byte)7 /* BinaryType.PrimitiveArray */ })
             {
+                yield return new object[] { recordType, binaryType, (byte)0 }; // value not used by the spec
                 yield return new object[] { recordType, binaryType, (byte)4 }; // value not used by the spec
+                yield return new object[] { recordType, binaryType, (byte)17 }; // used by the spec, but illegal in given context
                 yield return new object[] { recordType, binaryType, (byte)19 };
             }
         }