From 581b0a1cedcdb474c6369a6fc395ac68ece63921 Mon Sep 17 00:00:00 2001
From: Louis Seubert <louis.seubert.ls@gmail.com>
Date: Sun, 12 Jul 2026 18:43:37 +0200
Subject: [PATCH] fix(validation): return no problems for null reference
 instance in Rule.Validate

Rule<T,TProperty>.Validate cast a null instance to T and validated it, so a
reference T whose accessor dereferences the instance threw
NullReferenceException on a direct validator.Validate(context) with a null
instance. Guard the null-instance path and return no problems instead.
---
 CHANGELOG.md                                   |  1 +
 src/request.validation.tests/ValidatorTests.cs | 11 +++++++++++
 src/request.validation/Rule.cs                 |  2 +-
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index a7ba39b..c2c6fb0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -52,6 +52,7 @@ To have a consistent experience across all packages, some public interfaces have
 - **request.result:** Correct the namespace in the `Prelude` doc comment (`Geekeey.Extensions.Result` → `Geekeey.Request.Result`)
 - **request.result:** Fold `IsSuccess` into `Result<T>.GetHashCode` to avoid collisions between a failure and a success value whose hash is `0`
 - **request.validation:** Guard null comparison bounds in `GreaterThan`/`LessThan`/`Between` etc. so a `null` bound no longer throws (`NullReferenceException`)
+- **request.validation:** Return no problems when validating a `null` instance of a reference type instead of dereferencing it (`NullReferenceException`)
 
 ### Removed
 
diff --git a/src/request.validation.tests/ValidatorTests.cs b/src/request.validation.tests/ValidatorTests.cs
index 14239f7..6613720 100644
--- a/src/request.validation.tests/ValidatorTests.cs
+++ b/src/request.validation.tests/ValidatorTests.cs
@@ -45,6 +45,17 @@ internal sealed class ValidatorTests
 		}
 	}
 
+	[Test]
+	public async Task I_can_validate_with_a_null_instance_without_throwing()
+	{
+		var validator = new PropertyValidator<Person?, string?>(person
+			=> person!.Name, rule => rule.Must(value => value is not null, "Name is required."));
+
+		var result = validator.Validate((Person?)null);
+
+		await Assert.That(result.IsValid).IsTrue();
+	}
+
 	[Test]
 	public async Task I_can_compose_nested_validators_and_aggregate_property_paths()
 	{
diff --git a/src/request.validation/Rule.cs b/src/request.validation/Rule.cs
index 0c65cc0..a6a397c 100644
--- a/src/request.validation/Rule.cs
+++ b/src/request.validation/Rule.cs
@@ -46,7 +46,7 @@ internal abstract record Rule<T, TProperty> : Rule
 
 		if (context.Instance is null && default(T) is null)
 		{
-			return Validate((T)context.Instance!, context);
+			return [];
 		}
 
 		var actualType = context.Instance?.GetType().FullName ?? "null";