feat(result): refactor result handling to use private fields

- Replaces public properties with private fields in TryPickResult and TryPickProblem methods for improved encapsulation.
- Adds a new test case for handling null values in TypedResult, ensuring correct behavior when results are null.

Author: winromulus

src/ES.FX/Results/Result.cs

@@ -103,8 +103,8 @@ public Result(Problem problem)
     /// </summary>
     public bool TryPickResult([NotNullWhen(true)] out T? result, [NotNullWhen(false)] out Problem? problem)
     {
-        result = IsResult ? AsResult : default;
-        problem = IsProblem ? AsProblem : null;
+        result = IsResult ? _result : default;
+        problem = IsProblem ? _problem : null;
         return IsResult;
     }
 
@@ -119,8 +119,8 @@ public bool TryPickResult([NotNullWhen(true)] out T? result, [NotNullWhen(false)
     /// </summary>
     public bool TryPickProblem([NotNullWhen(true)] out Problem? problem, [NotNullWhen(false)] out T? result)
     {
-        result = IsResult ? AsResult : default;
-        problem = IsProblem ? AsProblem : null;
+        result = IsResult ? _result : default;
+        problem = IsProblem ? _problem : null;
         return IsProblem;
     }
 

tests/ES.FX.Tests/Results/ResultsTests.cs

@@ -5,6 +5,24 @@ namespace ES.FX.Tests.Results;
 
 public class ResultsTests
 {
+
+    [Fact]
+    public void TypedResult_CanBe_Null()
+    {
+        var result = TypedResultAsNull();
+        Assert.True(result.IsResult);
+
+        if(result.TryPickResult(out var resultValue))
+        {
+            Assert.Null(resultValue);
+        }
+
+        if (!result.TryPickProblem(out var problemValue))
+        {
+            Assert.Null(problemValue);
+        }
+    }
+
     [Fact]
     public void Result_CanBe_Success()
     {
@@ -103,4 +121,7 @@ public void Results_CanBeEqualityChecked()
 
     private static Result<string> TypedResultAsProblem() => new Problem();
     private static Result<string> TypedResultAsValue() => string.Empty;
+    private static Result<object?> TypedResultAsNull() => (object?)null;
+
+
 }