Fix bad serials (#304)

- [X] Fixes bad serial calculations
- [X] Tightens HexStrings

Bumps release version
Updates documentation

Projects/Server.Tests/Tests/Utility/StringHelperTests.cs

@@ -0,0 +1,18 @@
+using Xunit;
+
+namespace Server.Tests
+{
+    public class TestStringHelpers
+    {
+        [Theory]
+        [InlineData(null, "default value", "default value")]
+        [InlineData("", "default value", "default value")]
+        [InlineData("this is a valid string", "default value", "this is a valid string")]
+        public void TestIsNullOrDefault(string value, string defaultValue, string expected)
+        {
+            var actual = value.DefaultIfNullOrEmpty(defaultValue);
+
+            Assert.Equal(expected, actual);
+        }
+    }
+}