refactor: remove unreachable default-value branches

src/NetEvolve.FluentValue/Constraints/DefaultConstraint.cs

@@ -8,7 +8,7 @@ internal sealed class DefaultConstraint : ConstraintBase
     public override bool IsSatisfiedBy(object? value) =>
         value?.GetType() switch
         {
-            { IsValueType: true } valueType => TypeExtensions.GetDefault(valueType)?.Equals(value) ?? false,
+            { IsValueType: true } valueType => Equals(TypeExtensions.GetDefault(valueType), value),
             _ => false,
         };
 

src/NetEvolve.FluentValue/Constraints/NotDefaultConstraint.cs

@@ -8,7 +8,7 @@ internal sealed class NotDefaultConstraint : ConstraintBase
     public override bool IsSatisfiedBy(object? value) =>
         value?.GetType() switch
         {
-            { IsValueType: true } valueType => !TypeExtensions.GetDefault(valueType)?.Equals(value) ?? false,
+            { IsValueType: true } valueType => !Equals(TypeExtensions.GetDefault(valueType), value),
             _ => true,
         };
 

src/NetEvolve.FluentValue/TypeExtensions.cs

@@ -4,18 +4,6 @@
 
 internal static class TypeExtensions
 {
-    internal static object? GetDefault(this Type value)
-    {
-        if (!value.IsValueType)
-        {
-            return null;
-        }
-
-        var underlying = Nullable.GetUnderlyingType(value);
-        if (underlying is not null)
-        {
-            return null;
-        }
-        return Activator.CreateInstance(value)!;
-    }
+    // Nullable<T> yields null from Activator.CreateInstance, so no explicit handling is needed.
+    internal static object? GetDefault(this Type value) => value.IsValueType ? Activator.CreateInstance(value) : null;
 }

tests/NetEvolve.FluentValue.Tests.Unit/TypeExtensionsTests.cs

@@ -7,7 +7,7 @@ public class TypeExtensionsTests
 {
     [Test]
     [MethodDataSource(nameof(GetDefaultData))]
-    public async Task IsNullableType_ShouldReturnTrue_WhenTypeIsNullable(object? expected, Type type)
+    public async Task GetDefault_ShouldReturnExpected(object? expected, Type type)
     {
         // Arrange & Act
         var result = TypeExtensions.GetDefault(type);